I can understand that. It's a lot of work.
I do it manually. I like it to get a balance of career and peak WS numbers. I usually rank my players based on this.
Here it is
1) total win shares (career win shares/10 to the harmonic mean of 25)
2) average win shares in the top 3 seasons
3) average win shares of best 5 consecutive seasons
4) average win shares per 162 games (per 43 starts for pitchers)
Here is a link to the excert...
The New Bill James Historical ... - Google Book Search