Just a thought, but is there some possibility that civillian people could be used in a surveillance capacity? It would be dicey duty, much like a recon assignment, with the purpose of identifying, tracking, and tipping off the officers to intervene, not engaging or confronting the invading illegals.
This would be more along the lines of a traditional 'Neighborhood Watch' group.
The use of civillian volunteers could give official agencies the ability to coordinate/regulate the actions of the volunteers (which effectively ties down all but the most loose cannons), while augmenting security forces.
It would also give the locals an outlet for the need to 'do something' without things getting out of hand.
The feelings of fear and helplessness otherwise will only lead to the formation of more (uncoordinated) patrol groups, and increase the potental for animosity between landowners and official agencies, a situation which benefits no one but the illegals.
Right now you have lemons. Make lemonade. Turn what could be a disadvantage into an advantage.
I could think of a few, but like you said, it would be dangerous. The drug smugglers and human smugglers have qualms at shooting folks, uniform or no uniform.