Non-Amazon Book Plugins?

I don’t think that Amazon is the be-all and end-all of online bookstores. I much prefer to send my money to other, more independent places, like Powell’s or Alibris or something. The tricky thing about this in blogging, though, is that all the plugins seem to be built for linking to Amazon. Are there any that provide alternatives? Is there any easy way to modify the existing plugins to link to Powell’s or something, instead of going straight to the big octopus?