Free? Ha ha ha.... They couldn't run a profitable business if they were even to let you exchange it for the difference in price. I remember two months ago, and everyone on these MacBook Pro boards was aware that the Core2Duo (Merom) chip was going to be added to the MacBook Pro models in a short time. For some reason you figured you could live with out the upgrade when you purchased your laptop, so I suggest you do just that.
The only option you have is to eBay/sell your laptop and put that money towards a new model. A somewhat expensive proposition.