Since it does not cost anything,
try the trick “emergency semi-locker differential”
where you click down the parking brake pedal a few notches
shift into number one gear
and slowly move forward with your left foot slightly pressing the brake pedal
and your right foot carefully working the accelerator pedal.

The idea here is to apply enough torque to constantly move the rear axles even though both sides brakes are hindering but not entirely stopping motion.
One side’s wheel driven by your open differential will lose traction first,
and normally would wildly spin and consume all the engine power,
preventing other wheel with more grip from slowly moving the truck forward.

You will have to experiment to find the best number of emergency brake clicks and left foot braking pressure.

Traditionally you also put all the 4 truck floor mats down on the ground in front of the tire that turns out to have better traction to provide a “grip road” and have an assistant shuffle each floor mat run over to the front of the line again.

But this can dirty and even damage the mats.
Bath towels, old carpet, front door mats also work.
Chain link fence sections have been taken down and used, etc.
In mining areas worn out conveyor belt strips are plentiful. Check local rock quarries.