I've tried it. I had a Hobie 18 compost and also could not find a way to seal the junction between aluminum and compost in the luff groove (kerf). So I istalled a bycicle tire valve at the front of the mast, just above the mast base fitting.

I also saw a need to let in air so that the water would come out, so I routinely pressurized the mast with a bike tire pump before letting water out; this sped up the exit of the water.

I chose a presta valve because it was the smallest diameter valve that I could find at the time. I would prefer the schrader valves used on automobile tires because of their rubber to mast fit, but I was reluctant to drill a hole any larger than necessary to get a valve in there.

If I were to do it again, I'd probably go ahead and use a car tire valve. See a tire buster at a local car repair center for intallation instructions and perhaps to borrow a tool to do so.

GARY