the arca-swiss system is available on just about anything and if the ball head you're looking at doesn't use it you can usually swap out the top place for someone else's and get one that allows arca-swiss plates. There are some modifications but the basic flange design used by Arca-Swiss, Wimberly (I think that's the name), Kirk and RRS among others is basically all the same. I use Kirk plates on a Markins head, it's all fairly standard.

A friend of mine is a mechanical engineer and he's got a D3 with a Kirk or RRS L bracket, he felt that to do it himself would be no more economical (counting time and materials) than buying one from one of those guys. I imagine he's probably right but best of luck to you and I hope you can make it work well.

these are Kirk's L brackets
http://www.kirkphoto.com/lbrackets.html

Others make them as well.

As far as my friend's design, I don't think he made one up. He looked at the designs, contouring it properly, etc and decided it would just be a waste of time and buying one from someone (like Kirk or RRS) made more sense.

I built one up in CAD but i never got anyone to quote on it. Mine wasnt all that special, just 1 long metal plate bent at the right place with 2 dove tails, one on each side.
If you are successful in making one, I would pay for a 2nd!

It's a lot harder when you're trying to fit it around a slide-in battery (like pro Canon or Nikon bodies) in addition to the connectors than if you're just trying to fit it around connectors.