Absolutely, the choice of back-end can become a simple config item. I'm a little (ok, more than a little) makefile-challenged, so I need to hit the books on this.

The further bit of complication is that whichever data store is used must have a bit of pre-configuration done before the test suite can run (hmm... maybe I can set up a "test" that does this, which can run as the first test....).
This would make the pick-one-at-make-time a good option.