I would have expected in the above that you should have been able to place him on the major league roster and then the MLB disabled list. I know in the past I've also simply used one click to add him to the secondary roster, and then he should be able to be dragged to the DFA list (if you don't have an open spot on the MLB roster).
Putting him on the minor league DL is not really supported behaviour, since if he got hurt in the MLB I would imagine that the MLBPA would have a problem with trying to send him down and put him on the minor league DL. But I guess sometimes it would be nice to have a bit more explanation for what might actually be possible to do with a player, since it's understandable that not everyone is a CBA expert.
Also, stay safe
