?? Why not?? Lighted cars need a pickup added for the center. Non powered cars shouldn't pose an issue. (correct me if I'm wrong but G is 2r, St is 3r, both are the same gauge... or is it 1gauge or wide gauge?)
Two rail type wheels must be electrically isolated from each other, so are plastic or have an isolating instert in the wheel hub(s).
So, say you can fashion or buy/ mount a center pickup shoe, that goes to the bulb, new wire, remove the old on that end only. Now take this old wire and attach it to the other bulb terminal instead, combining both wheel's wires to double the the number of wheels contacting the outer rails.
Plastic wheels? Shoes on the outer rails near wheels are another 2r trick we don't see as much in O. So are "wiskers" which can be nice thin phos/bronze or a scrap of solid copper wire, etc.. (hide behind wheel somewhat, then fwd or back so it contacts the side of the rail head along the flange rub, close to the wheel. I used a wisker in this bash because I wanted to lower the O height with S scale plastic wheels. Needless to say there is near zero effort in hiding it here. It just worked so well I never bothered to do it "right".