Silicone, you mean RTV? I wouldn't think that's strong enough for a pretty permanent installation.

On the taillight, I'm planning to run the return current throught fender stay, which is bolted to the dropout and seatstay, where the bottle dyno is mounted. I'm not real worried about the tail ground, though the return wire is the most reliable approach. But on the headlight, the ground runs through tthe headset, and I think that's perhaps a little less reliable than the chainstay, even though it works now.