I watched a number of the trucks at this years Dakar use this type of jack to lift their huge rigs to make repairs. If these bags can take that abuse, then they can easily handle a 4Runner. Sure would be an easy way to lift the 4Runner to make a fast tire repair.
I have a tire plug kit. So, I doubt that I would change out a flat tire for a spare. But it is a whole lot easier if you can lift the 4Runner, put some aire in the tire, and spin it to see where the hole is. Then reaming and inserting the plug is a lot easier. I think the Bushranger X-Jack is the hot ticket for this use. Even better it lies flat on the floor until needed.
In the front I would position the bag under the skid plate. In back, I would place the bag under the spare maybe? Not sure.