It is a PAIN IN THE BUTT. I may start using smaller jugs to avoid it.
If it's truly roasting outside, keeping it in a car in the sun an entire day may do it, but I've only got a partial melt that way (and even with coconut oil which has a lower melting point). (I found a pail of coconut oil, which admittedly I'd used up very slowly, also had serious separation of stearic acid and I had had some inconsistent soaping results so I decided to treat the coconut the same way)
I have made a giant double boiler by putting a big speckled canning pot on the stove, putting in a couple blocks of wood, heaving the massive pail into the pot, filling the canning pot with water, and heating away. It takes a looong time so combining it with the car thing may help. It will also seem all melted when there's still a core of unmelted stuff.
In future I may try filling every big pot with part of the pail, melting it all then pouring it back into the big pail to mix it, then doling it back out into containers. But then I will have a million pots to wash
Also, a friend gave me what she called a birdbath heater when it's actually a stock-tank heater, and I wondered if that could handle immersion into oil! If so, that should do well, I think! (never used one before for anything but I'm sure I should keep it from touching the plastic bucket)