I have had several of the Dual 50 Headlight lenses out and I never had to do melt anything. In fact, I wouldn't put heat near the lens or you might ruin it. I have seen lenses that melted due to the owner running a high wattage bulb in them. A friend of mine that was a huge Dual 50 fan said to only use 15 watt bulbs. To get the lens out, just press on it, I believe from the bottom. It just pressure fits in the hole. I don't believe glue or anything else is needed. Good luck!
Chad