The easiest way to keep the pace under control is to find a slower friend who is running and pace them - or make a new friend early in the race who is running an easy pace for you and run with them. Barring that make a game of it seeing how close you can hit a preset pace.

This is what worked for me at my 20 mie race before my marathon.  I wanted to run it easy, since it was only three weeks before the marathon.  So I ran the first half with a friend, chatting the whole time, then picked it up on the back half and tuned it into a progressive long run.  She helped me slow down, and I helped her speed up a lil (she was racing it).

 

So you are suggesting I hire a film crew and make a documentary of my journey?

At the very least, write a book about it.