I've done lots of tires like that, always with starting fluid/ether. It's not really inflating it, it's reseating it on the bead. Running 36" plus tires on 15" rims at low pressure means you will pop a bead in the rough stuff from time to time.
Less common on the newer 16, 16.5 and up rims. Also rock crawlers run so low on the rocks they use beadlocks which prevents the problem in the first place.