Wait: so you're not dead?
Also, if anyone knows of a way to put 3 summon monsters on one summon materia, that would make me happy, but that's a dream, and I don't know if it's possible.
You can't do it with Wallmarket, that's for darn sure. Summon materia can only allow one attack; you'd need to seriously mess around with the hard-coding for it to do anything else (by "seriously", I mean that it wouldn't simply be a case of disassembling and changing one hex value).
EDIT:
Should this be in general? That last bit makes it sound like more of a Reverse Engineering question.