If this "Activist" group contains, or knows any Mexican citizens, they could (theoretically) license their station in Mexico, and "border-blast" their programming into San Diego...
Two things, I think, would prevent this (other than the technical issues of available channels):
First, Mexico does not reserve any portion of the FM dial for non-commercial stations, so were there a channel available, the large groups would snap it up.
Second, Tijuana is a top 10 market in Mexico, so a license would have great value (despite the fact that some of the longer-lasting family groups are less than stellar in their administration of stations).
Add in the issues involving the need for legal representation in Mexico City, knowledge of the way the, ahem, system works, and such I really doubt that these folks could ever get a license in Mexico.
In any case, I'm still not quite sure what the group stands for. It's easy to see what they are against, as even their website header graphic is a bunch of people with placards protesting. It will be interesting to see how they develop programming for the license(s) they get in S.D. County. They seem to have a concept of developing programming in a free form, open, group. I'm reminded that a camel is a horse built by a committee.