Just thinking as I type here Bill. What about priming the inside of each half with epoxy and matt then, while wet, inserting a wetted out matt of carbon wrapped around some kind of bladder/tube that you can inflate while it cures?

If you had to introduce a tube or two through the mast wall you'd be able to repair these holes afterward. You might be able to get some kind of polythene sleeve of the right diameter from a packaging supplier? It would only have to be approximately the right diameter, over not under.

Of course I may be way off base but that's the sort of aproach I'd take to get an initial repair and then I'd finish off on the outside.