I doubt that you could train an army to fight against them, but an elite group of commando-type fighters might be able to make a difference. The problem is doing it within the "Rules of War", if there is such a thing. I think the only real way to fight that kind of battle is to infiltrate the guerrilla groups and execute their leaders, as brutally and publicly as possible. Don't try to capture them, don't try to reason with them, don't ever let them off the hook. You go in and grab hold and kill them, one at a time or in groups, until the units wither away and die.
It wouldn't be pretty, it probably wouldn't be legal and, if the US news media found out about it they would castrate (figuratively, hopefully) the soldiers doing the work, the generals who sent them out and the lawmakers who appropriated the funding. But if you consistently take out the leadership you will eventually have a group of guerrillas who won't know how to carry on fighting.