I have taken Epsom Salts but not with this flush protocol. My directions were to drink mag citrate, so I've always done it that way. I'm a stickler for following directions.
I think Epsoms Salt would work though... as long as you don't have a bad after-effect from the Epsoms Salt. Just be sure to take enough - I have no idea how much that would be. The body can probably handle smaller amounts spaced out than one large dose.