There is always a way to implement something with all respect, it takes just a constructional inventive mind and development to implement it. The same way a player can purchase VIP of some sort on their account it can be the same way. I believe the same way game websites allow for voting, and the voting website returns the person to their account page where they are debited with whatever reward it is for voting by the game website. I believe once a person chooses the paypal method, the same way the system captures what account to credit with the e-coins after the purchase is complete, is the same way a time-stamp and transfer reference number is available, and could be used as a match to figure out who are the culprits. For the players who are awarded with the trusted title, their paypal donate link would just be different, it's a simple code line to group them differently just instead of a normal "VIP" they could be in a special category by themselves. TL;DR i know but eh...
I just think that instead of crippling the one good way many persons would rather donate to your server, it would be wise to sit and R&D and find a way around it, because there is, it's just a matter of putting in a little work which clearly would pay off.
My two cents.