Kuldahar's temple doesn't offer restoration, so there are no ways to get rid of level drains from the vampire gnolls but to wait until your priest has acces to level 4 spells, right?
Nope, I added a special book out there, in the area where the gnoll vampires are encountered. It allows you to cast restoration. Furthermore, I think I added restoration scrolls in the temple, IIRC, so while it's not among their usual spells, the scrolls may still be available.