There is no way of overclocking it just yet but there is a way to reduce the clock speeds based on what you are doing. NO2CHEM came out with Nue Dynamic Clock. It can get the clock to reduce when the phone doesn't do anything for a 5 seconds or when the screen is off. Might reduce the heat issues. Here is the link:
Code
http://www.nuerom.com/BlogEngine/post/2009/04/20/nueDynamicClock.aspx
And it is donation ware so please donate accordingly if you use his product.