People will probably wander off with any small trinket-like light source. "Dude look what I found!" "Oh, sweet, where'd ya get it?" "Oh, just over there, there's a whole bunch..." (But maybe I'm too pessimistic) Fair enough. I guess we just need to make sure that the LEDs look like an integral part...

Maybe I'm crazy but how about magnets? Here's what I'm thinking: we use magnets to attach each pixel to its neighbors and to rebar anchors. ThinkGeek sells what they call 'Curiously Strong Magnets'. They're really just small rare earth magnets which are available for bulk purchase from several place...