Most smaller sailboats do it the same way. Every time out I pulled the mast crutch pole and stored it below deck. No need to go all the way through, just 4 to 6 inches is plenty. Here comes the tuff part so do it very carefully. I used a propane torch.
Plastic pipe is cheap.
While rotating the PVC pipe, slowly heat it about one foot above the base. When the plastic get's soft, bend it to about a 30-45 degree angle. Let the pipe cool so that it will hold the bend. If you get minor black ash marks, on the pipe try sanding them off else get another piece and start over. Mark and drill holes in the upper part of the pipe to match the eyelet distance on the flag.