Widgets are intended to be a quick, modular way to get some information about your league to your home page.  The modularity allows for flexibility, such as putting it behind a jQuery tabs, jQuery accordion, or something similar.
There isn't a way to specify additional stats to display with a player leaderboard widget.
Anyway, here is some documenation that should help:
OnDemand Widgets 
On‐demand widgets allow you to call some code to display snippets of data on your website outside of StatsLab. The script that creates them is widget.php, and by including a link to the widget.php file with the appropriate parameters defined, you can get a widget to display on your website that will automatically display the most recent stats after every SQL upload.
 
The following parameters can be applied to widgets.php to generate a widget:
- show: The “show” parameter defines what type of widget you want to display. The following options are available:- leaders - By setting it to ‘leaders’, it’ll display the top teams in each division in an unnumbered list format.
- standings - By setting it to ‘standings’, you can get the divisional standings for any division in your league (with additional parameters).
- draftList (need version 3.0.10) - By setting it to 'draftList', you can get it to display the progress of your StatsLab draft.  This has additional parameters:- lastX - tells it how many of the most recent picks to display
- nextX - tells it how many of the upcoming picks to display
 
- potw - Will display the current player of the week for the sub league specified.  Includes player photo, name, team, and some basic stats.
- botm - Will display the current batter of the month for the sub league specified.  Includes player photo, name, team, and some basic stats.
- potm - Will display the current pitcher of the month for the sub league specified.  Includes player photo, name, team, and some basic stats.
- rotm - Will display the current rookie of the month for the sub league specified.  Includes player photo, name, team, and some basic stats.
- Anything else, including omitting this parameter, will result in a listing of the top players in a specific stat (stat must be specified). 
 
- league_id: Specifies the league that you wish to display the widget for. Will default to StatsLab’s primary league if omitted.
- sub_league: Specifies the sub‐league you wish to display. Use the sub league’s ID number or abbreviation (if unique). If omitted, leagues will be combined. This parameter must be specified to display a division’s standings.
- division: Specifies the division you wish to display. Use the division ID as the value, and it must be combined with the sub_league parameter. It has no effect on player stat widgets.
- topX: For player stat widgets, this parameter defines how many players to display. By default, the top 3 players will be included.
- stat: For player stat widgets, this parameter defines which stat to display the top X of. 
The following stats are available for player stats widgets (note that this list is more extensive than for static widgets): 
Batting Stats: AB, H, 2B, 3B, HR, RBI, R, SB, CS, BB, K, SF, SH, IBB, HP, GDP, PA, AVG, OBP, SLG, OPS, wOBA, VORP 
Pitching Stats: W, L, SV, IP, K, BB, R, ER, G, GS, HP, HA, BF, GB, FB, HRA, BK, GF, QS, CG, SHO, HLD, ERA, WHIP, VORP 
To include any of the above stats, set the stat parameter equal to the lowercase version of the stat (e.g. avg=batting average), with the following exceptions: 
K, BB, R, G, GS, HP, and VORP for pitchers should be preceded with a “p” to differentiate them from the batter stat version (e.g.: k=batting K’s, pk=pitching K’s). 
Use “s” for SV. 
Examples:
- widget.php?stat=h&topX=7&sub_league=NL – Will display the top 7 NL leaders in hits.
- widget.php?stat=pk&sub_league=AL – Will display the top 3 AL leaders in pitching strikeouts
- widget.php?show=leaders – Will display the division leading teams in each division.
- widget.php?show=standings&division=1&sub_league=1 – Will display the standings for sub_league 1, division 1 (in my test case, the NL Central).
- widget.php?stat=ops&topX=10 – Will display the top 10 batters in OPS across all subleagues (e.g. All MLB, rather than just AL or NL).
- widget.php?show=draftList&league_id=100&lastX=5&ne  xtX=5 - Will display the 5 most recent picks, and the 5 upcoming ones
- widget.php?show=potw&league_id=100&sub_league=0 - Will display the Player of the Week for sub league 0
You can test your on‐demand widget out in your browser before adding the code to call it to your website.  If you wrap it appropriately, you can do some nice things with CSS for displaying it.
Widget CSS 
wdgT – Applied to <table> tags 
wdgH – Applied to <tr> tags contained inside <thead> tags. 
wdgH_l – Applied to <td> tags inside <thead> tags that might require different alignment. 
wdg1, wdg2 – Applied to alternating <tr> tags 
wdg1_l, wdg2_l – Applied to alternating rows <td> tags that might require different alignment 
wdgUL – Applied to <ul> tag in division leaders widget 
wdgLI – Applied to <li> tags in division leaders widget