You've got a web site, why not just use the email to direct people to a page, say, rtr.ca/payme, which would make users answer questions, and then only presents them with the proper email address given their answers to those questions? For instance:

Top page: I live in.... (US, Canada, Europe, etc.)
Next level: I will be paying with: (Credit card, Paypal balance, eternal gratitude, etc.)

That way, assuming they answer the questions properly, they don't even get the other Paypal address presented to them.