Yes, you could do that. A natural gas and air flame, such as from a Bunsen burner, should be good for that. That should "cook off" just about any dirt or oil on the coin and leave it very clean. This would have to be done VERY carefully, though, so as to not damage the coin by careless handling. Pt coins tend to be expensive items, so it would probably be best to minimize handling and cleaning. Perhaps a very gentle rub with a cotton ball and some isopropanol would be sufficient for removing any dirt or oil from the coin without causing damage to it.