I was just reading this article on cold water swimming:

http://triathlon.competitor.com/2011...wimming-2_9072

There's a few tips in there you could try.

My definition of cold might be a little different than yours considering I'm in the PNW and you're in Hawaii, but it's all relative - I might put on a wetsuit where you aren't. I definitely can feel the gasp reflex come on as I get in the water, worse the colder it gets, and have to breathe through it. In even colder water, my ears start to hurt.

You might also try a wetsuit (sleeveless?) or even just a farmer john swim skin that adds a bit to your insulation and glide while you warm up.

Hope you find a good technique!!