Could it be that the Basques were originally mostly G2a and then later were overwhelmed by a flood of R1b males?
I know this sounds bogus, but I actually thought of that possibility long ago when I saw some G2a guys in the Basque Project. I mentioned something similar on Rootsweb a few years ago, only I didn't mention the y haplogroup.
Anyway, yeah, I think that is a distinct possibility. Some linguists have noted similarities between Basque and some of the Caucasian languages.