Depending on your product, have you considered taking payment from the purchaser's mobile phone (even if it's just an alternative payment route), that way people without Paypal can still make a payment without having to leave your site while they sign up.

http://www.mxtelecom.com/uk/payforit#about http://www.mxtelecom.com/uk/tech/cta/webpfi

Just a thought, I work for these guys, so I can't claim to be impartial.