Given IMVU's development practices I think your problem is more like "Delete all those people who click on photos of big-chested anime girls in sapphic embraces." (Edited to add: I assume they go on to convert as well. sigh)

Heads up to every person who wants to run an ad-based startup: remnant inventory is the term for the inventory -- i.e. page views -- you have to sell after you sell those spots which are actually worth money. Remnant inventory is nearly worthless. The only people who will pay money for it are either a) idiots who will shortly exit the business or b) people appealing to the lowest common denominator.

If you don't want your website to be cluttered up with Punch My Scantily Clad Diploma Now, My Lord, then you should charge money for it.