Should be able to match based on individual headers, regex matches, specific request params, etc.
I'm not sure if this is helpful or not, but I recently rewrote this part of VCR and blogged about it:
There may be some ideas in there that'll be useful for betamax.
That's interesting, thanks. It appears to be similar to the approach I've already taken in https://github.com/robfletcher/betamax/blob/master/src/main/groovy/betamax/MatchRule.groovy I just haven't opened it up to allow the use of custom MatchRules yet.
Test proving that custom match rules are possible