If there's a reliable source of feeder gerbils in your area I suggest you offer those to the snake
Switching prey is rarely a good idea and can cause more than one problems.

Ball Pythons are imprint eater, if the animal imprint on gerbil he might never switch back, gerbils are expensive and potentially more dangerous than other rodents. (aggressivity + long sharp teeth) If the animal had to be re-homed someday this could be an issue making it impossible for him to find a good home.

Trying to find out the cause is always the first step than making necessary changes or be patient is the second step.