Why not look into online book clubs? These are avid readers and pretty enthused writers. I'm sure many would be pleasantly surprised at an offer to subsidize their discussions with a delivery of free books.
Here are some links to get you started in your search:
- The Book Clubs Resource A nice overview of some General Interest and Special Interest book clubs out there on the internet.
- Book Talk A very interesting forum dedicated to the intelligent discussion of non-fiction titles.
- Blogshares' list of book club blogs A good place to track growing (or declining) readerships.
- Book-clubs.com Self-explanatory!
Good luck, and let us know if this works for you.