What you are looking to add is the flexibility of maybe drafting a player and undoing the call up to make room. For me the key is to ensure you aren't burning a free year by taking a risk and calling up a rookie early.
I'm not sure that we're really saying the same thing, I think you're complicating it.
My suggestion is to simply designate a player as a Toews Rule player which puts them in limbo along with the automatic Toews Rule players where they don't count as one of your 20 farm players, they don't count as one of your 23 skaters at the auction and they don't count against the money you have available at the auction to sign your team. To me what you are describing is that they are part of the 23 skaters but their salary doesn't count which is different.