Probably not; that's just what I use when I'm making it on the stove, so I used it for this too. Butter would probably work just fine. Probably about a tablespoon; I'd recommend pre-melting it for about 30 seconds in the bottom of the jar, then add the kernels and swish them around a bit and go from there. I'm pretty sure it needs to be some kind of fat in order to absorb enough energy from the microwaves quickly enough, but aside from that I don't know that it matters.

Hmm... for something really decadent, maybe I'll try bacon grease next time... ^_^