Child Had Distal Radius Fracture, Open Reduction With Internal Fixation. Better Way To Rig Up Cast In Order To Play Soccer?

Hi, My son had a complete distal radius fracture on June 6.He had an open reduction with internal fixation on June 14, six weeks ago. He wore a short cast for two weeks, then had that removed and replaced with a velcro brace. My son is tryout out for his high school soccer team. The doctor wants him to put the cast back on to play soccer. We have been trying to find the best way to reapply it. So far, we have been putting a tube sock on his arm , then putting the two halves of the cast back together over that, and wrapping with a stretchy self adhesive ace bandage . We purchased a cast cover which meets HS regulations, but now we are having to trim the cast to get it to fit under the cover properly. The sock as underpadding is not working too well--too thick in some areas, too thin in others. Is there a better way to rig this up? We thought we would only need to do this a few times, but the doctor has extended the amount of time he s to wear the cast, so we will be doing this on many occasions. Thank you.