I ran the can under the tap to melt the ice, took the base off it with a tin opener and sat it on a little quiche pan in which I had placed a tealight candle. I sat a pie pan on the top to place the melt in and there it was - my tin-can melt warmer!
After a couple of minutes the candle snuffed it so I ended up drilling some holes near the base of the can to allow the candle to draw more air. It now works brilliantly! Next time I will try a more intricate design, perhaps a willow tree? And I think using a bigger nail would work well too.