My thanks to nwhyte for his offer to help, but I've (slightly to my amazement) managed to persuade the Dupuytren Society to add a Paypal button to their web site.

There's no incentive like saying "I'll send you x Euros, if you can get Paypal to work on your site in English".

So, I've just sent them x Euros.  Without the advice of the Dupuytren Society, I would never have sought out radiation therapy for my right hand.  The hand is as good as it was the day it was treated and I've never looked back.