The problem with that is, like Stinkubus said, the roster-checker requires you to keep at least one FS (that's actually listed at that position, not just depth charted into it). So you'd still have to keep a FS on the roster either out-of-scheme, or with stats that are less optimal than they could be.
It's one player, and scheme XP is less than it used to be, so it wouldn't end the world or anything, but the most optimal approach is getting a scheme fit FS and just putting all their upgrades in RS.