I tried the quick link and got the same message, even when already logged on to PayPal. I then clicked on Ben's webpage link, clicked on the "Donate Now", and just copied Paul's PayPal link from there, then pasted it into the PayPal "send money" page I already had up (Just ordered my t-shirt!). Seemed to work okay then...
I'm guessing the easiest way would be just to put Paul's (email or eBay ID) name on the Mosfet page. It's Mosfetational!!!