I think if your plastic plant can get hot enough to melt, your lamp is too close to anywhere your snake could go. Anything got enough to melt plastic is not somewhere you'd stick your hand; if it's too hot for your hand, it's too hot for the snake. If you're worried, hold your hand up to the lamp at the distance of the plant for a few minutes. If that doesn't hurt, the plastic plant is not going to melt.