I've yet to experience a blow out that the entire tire came off the rim. Not saying it can't happen. But usually there's enough tire left that it can make contact with the ground enough to break the lugs loose, or you can wedge something under it that will help it grab. But here are some suggestions that may or may not work.
1. Carry blocks of wood or other material that can be stacked high enough so that you can lift the rim in question, block it up, then let the rim back down on top of the blocks to hold it to break lugs loose.
2. Not sure if they have enough extension to them, but possibly use one of the "X-Chocks" that fit between the tires. If it will extend far enough, it should add enough leverage to hold the wheel. Can possibly stick a board or something in to make up the gap if needed.
3. If you have a passenger, have them hold the brake on the truck just long enough to break the lugs loose.
4. In a real pinch, remove other tire(s) on that side then lower the trailer until wheel rests on ground.
5. Buy a cordless impact wrench to keep in your tool kit, then you wouldn't need to worry about it.