As much as I have been hooked on Vocaloid stuff, I also wouldn't be sure if an mep would work too well. It sounds like a neat idea (no pun intended), but I find that a lot of people that watch or listen to Vocaloid video/audio enjoy it because they know what Miku parodied and not too much on the visuals. That, and the visuals usually that are put with vocaloid videos are usually a still frame or show the parodied anime/game (meaning the viewers don't care too much). But that's where this mep may be different and maybe come up with something really interesting.
Also, it might be important to say which type of Vocaloid parody songs you are planning to use:
actual sound parody
or
just voice parody
or both? o.o