I think this thread I posted up a few months ago might also help you out (and thanks to nicoga3000 for posting the links to the main thread that I did!):

http://pinside.com/pinball/forum/topic/tron-fibre-optic-ramps-how-to-fix-the-dips

Sorry for the late reply, haven't been on Pinside much lately (coaching 2 baseball teams 7 days a week)!

You are correct, I used the 1/16 bit to drill the pilot holes from under the lip and then I flipped the ramp over and drilled the larger hole from the topside (with a bit larger drill bit). To figure out the drill bit size to use is easy, just place the drill bit over the zip tie and all you'll need is a drill bit that's the width of the zip tie.

A good thing to keep in mind is that when you drill the holes back down from the top side make sure not to get the drill bit too close to that center channel as you drill down. If you do it's pretty easy for that drill bit to make some marks on your ramp channels. Just remember to drill straight down!