To add Gratipay to Blogger, use the gadget from gratipay.xml. Go to your blog overview, then:
Layout -> Add a Gadget -> Add your own
Enter URL ('https://' prefix didn't work for me):
grtp.co/v2/blogger/gratipay.xml
Set your "Team slug on Gratipay" and view how it looks on your blog page. Blogger preview didn't work correctly for me, so don't pay attention to it.