According to Gamblin Colors:


Instead of adding Gamsol to Cold Wax Medium to make it easier to apply as a varnish, we generally recommend warming the container to gently soften the wax.  Cold Wax Application:
  1. It is easier to apply CWM as a rubbed-on varnish if you warm it by placing the container with lid on outdoors in the sun or in a pan of hot tap water. (The goal is to soften the wax without melting it.)  Softening the stiff paste allows for it to be spread more easily over a broad area.
  2. Warming will accelerate the evaporation rate of Gamsol out of the beeswax, so adequate ventilation should be observed.
  3. Pat a small amount of wax onto a soft, lint-free cotton cloth and thinly rub it on to the oil painting using small circular motions.
 Adding Gamsol would also soften the beeswax and make it easier to spread, but the additional solvent increases the possibility that some of the painting may dissolve or lift in the process.  I would encourage you to experiment on a sample painting to test out the idea first.  Also, brushing on thinned Cold Wax Medium is likely to yield a different look than rubbing it on with a soft cotton cloth.   Again, test it first and allow the wax to dry completely before judging it’s final appearance.  Adding solvent and brushing on a coat of wax may take longer to dry if it is applied more thickly.