I hate to be obstinate, but why not giving BeWeDOS (or SpartaDOS if you have the MyIDE Rom) a try?
All the things you want, are able then, and you don't have to do things the unhandy MyDOS way.
If you need any help, you could contact me. Even on MSN or AIM.
I guess you want to be compatible with the great GameLoader made by Hiassoft. It is a good reason to use MyDOS indeed, but for Bewe/Spartados there is a similar game/demo/binary/loader available with same compatibility results.
Hehe... but again: I don't want to force anyone into the Sparta or BeWe Dos Scene
Perhaps I should make a nice website (with movie) to promote this wonderful Dos.
Good luck
Marius