A few guys over at BbL forum have done the mod to the bridge, and rave about the results- like a super big, clear focused B. Given the design of G&L's bridge, once the mod is done, you have acoustic coupling to the wood that rivals the whole 2Tek thing- without adding a whole pound of weight. And, the mod is reversible, tho I don't know why anyone would want to after hearing the result.
As for the original question, TI's will work through the back, as will Chromes. Now, as a suggestion, try DR SunBeams. IMO, the best string for fretless G&L's, after a great deal of experimenting on my ebony board L2000. Nice and warm, but with definition on the leading edge fo the note- you get all the fundamentals and overtones instantly, and still get a round but defined sound. After two years, there was a bit of ghosting on the ebony board, but no divots or grooves.
And, here's a kind of off-the-wall idea, Fender Tapewounds....smooth like glass, but still have some bite when you dig in. Flexible enough to go over the bridge, too. And relatively cheap!
