Set the tractor brakes; release the trailer brakes; hit trailer brake drums with hammer.
Don't have to hit the drum too hard either and the brakes shoes should pop loose from the drum.
Just don't try and be Hercules! Because you can crack the drum, after you set the brakes and then release them, pump them a couple times, find a block, to place behind the tire, release the brakes and tap on drum, they should release