By popular demand, I've added <a href="http://www.davidchart.com/Novels/Tamao/donations-in-multiple-currencies/">a page to let you donate in different currencies</a>. The default currency, for the links in the sidebar, is still yen, because that's the currency I will actually count the donations in. Unfortunately, PayPal won't let me associated multiple currencies with one button, so this appears to be the best way I can do it.

I hope people find this useful.