Herobizkit
Adventurer
Being penalized mechnaically (or "left out") for choosing a character outside of your campaign's style choices certainly might rub me the wrong way. I happen to be one of those play-along types, though, so if you (as GM) asked me to make a human, I probably would. I'd still want to be a Bard, though. 
If you really want to be heavy-handed about it, just explain that your campaign is humanocentric to the point of snobbery. Any non-human races will be seen (and treated) as slaves or property. Non-humans will be charged double, triple, or flat-out refused goods and services. Basically, give 'em the Drow treatment, but don't let them "put up their hoods" and suddenly disappear from scrutiny.

If you really want to be heavy-handed about it, just explain that your campaign is humanocentric to the point of snobbery. Any non-human races will be seen (and treated) as slaves or property. Non-humans will be charged double, triple, or flat-out refused goods and services. Basically, give 'em the Drow treatment, but don't let them "put up their hoods" and suddenly disappear from scrutiny.