I did my HIN like Danny, except I printed straight, not reverse. Worked fine as well. It is very slightly visible - mostly that the grain underneath is not as well-defined. Farther than a couple of feet, and unless you are looking for it, it's invisible.

They make stuff to create waterslide decals on an inkjet printer - saw kits in the art store. Seemed kind of expensive, and I don't know how they'd behave under glass and epoxy. Might be something to look at, though.

Dan.