Hey now, don't steal my first option I wanted to try. Kind of the TOM trick. I don't think that will work though as their isn't much room to place a small mirror back there to where you can see it. It would also be height sensitive (meaning only people of a certain height will see it).
For you pro owners - This is my suggestion.
- Go to comment pinball and buy 2 of these in the 555 style.
http://www.cometpinball.com/MATRIX-1-SMD-5050-FLEX-6-3V-QUICK-CONNECT-p/mtx1smdflex.htm
- then pick up 2 of these
http://www.cometpinball.com/6-3-V-Plug-Play-Strips-Comet-Pinball-p/6.3vsmdstrips.htm
The first light you will point straight up so that it lights the insert. The second part (the strip) you mount to the side of the switch guide (hole where the switch wires goes through). This will effectively light the hole up that corresponds to the insert. Everyone should be able to see the switch hole so that will now be your reference point for which lane is lit. Basically the same trick a lot of us did on our Avengers machines before the see through plastics came out.
For Prem/LE owners - we have light boards there. We will have to solder in another light there to do the same thing. Before doing that I want to brainstorm a bit more as I don't want to do more permanent type mods like that to the game at this point.