This isnt a post about making reinc exp count towards rebirth.
(although that would be nice, as other people have said)

How about giving your rebirth exp/15 as ability exp?
So 1st rebirth at 150M gives 10M to spend on racial abilities.
3rd rebirth total of 675m gives 45m worth etc.

This would allow you to choose non-rebirth races, get the
-exp rate penalty, but get a couple of "free" bonuses to
that race.