I've found a cheat site describing the space in the saved game where the captured monsters are stored, and fiddled around with monsters a little... With 9 Erikas, 4 Ur-Basilisk and a Drake Lord, the game can get rather fun for a short time.
Just one advice: Never try it with Doomguards. When they split, the copy is set to default - ie. hostile. I summoned five of them, one of them split and they proceeded to take each other (and my party) apart.