I just found some handy fork/brake mount light holders for Lumotec lights at Harris Cyclery's site that look pretty sturdy and handy for use with a homebrew light solution. There's a mount for canti brakes and one for caliper brakes:
Looks like they'll work perfect with my homebrew lights - though I will have to wire up a remote switch for them as they'll be out of reach. I could even see how you could use two brackets, connected to each other, to mount two lights from a single mount point.
Harris sells the brackets for $1.95 each (some heavier/sturdier ones for $4.00) - I just tacked them on to a recent order cause they looked like they might be useful, turns out they're perfect - solid and helpful to make more room on my cluttered handlebars. Hope this might be helpful to any of you folks out there looking for a solution to mount your single, or additional lights.