My 15 year old was diagnosed with a VM about 4 years ago. The doctors discovered it after she began activity after fracturing the growth plate in her left heel. Her calf muscle became larger than the right one and she was in so much pain in the morning that she couldn't walk. The pain would eventually subside, but it was very frustrating. I am sure all of us can relate with the frustration of proper diagnosis. It took the doctors nearly 6 weeks to discover what it was. Finally, it was a relief to finally work with a team of doctors who knew what they were dealing with and could offer some advice for symptom relief.
She began sleeping with a compression stocking and with her leg slightly elevated - this greatly relieved the pain in the morning because it reduced the clotting in the VM. She also began low dose aspirin therapy (81mg) and that helped as well. She took tylenol for the occasional pain she felt - which would usually happen when she did an excess of jumping (she is a competitive gymnast). The doctors monitored it by doing Ultrasounds and MRIs and didn't want to intervene until it became symptomatic to the point of limiting her activities. It has not changed size during this time, which I guess seems to be a good thing?
It did get to that point this past year and she had sclerotherapy done almost two weeks ago. She is still recovering from the procedure, so we won't know how successful it was.
If he feels relief while wearing the compression sock, then he should try to wear it all the time. I know it's hard to get a child to follow directions, but it will help. He could also try sleeping with his leg/foot slightly elevated. I would speak to your doctor about the aspirin because of his age. This may buy you some time and him some relief from pain.
Good luck with everything.....