Even getting one finger inside can help a little, but you'll probably need to start with this:
Try to do this twice a day for about ten minutes each time. Every time you pee throughout the day, give the end of the foreskin a good tug, strethching the side of it on the bottom.
These two exercises will loosen up the skin so that you may get to the two finger stretch. Now to find that stretch, you'll need to start reading all the threads on this page. You'll find a link to a page which outlines it.