Wow. I'm just going to take one word out of shaw's post.
How can there have been so many posts to this thread without mentioning aerodynamics? Isn't Myron's Mopeds the shop with the fully-faired Tomos?
Full-tuck does not equal fully-faired. What are you tucked behind?
I'm sorry to all the little men giving the big man advice on boosting his power output, but I think that perhaps the big man needs to try a front fairing on his awesome Pinto.
"This book":http://books.google.com/books?id=0JJo6DlF9iMC&dq=David+Gordon+Wilson&printsec=frontcover&source=an&hl=en&ei=lHG6SentLM-jtgf3wrjkDw&sa=X&oi=book_result&resnum=4&ct=result#PPP7,M1 gives a number of rather fantastic explanations why this is a good idea.
To paraphrase: A human body is not particularly aerodynamic. A bicycle or motorbike acts against the inertia of the air it has to move, though, in effectively only one direction. You can mitigate a human's un-aerodynamic nature by taking it entirely out of the equation - e.g. by "hiding" it behind a cone of air created using a small, leading fairing.
More aerodynamic means less power required to jump from 40 something to 50 something means that all the smart and tricky things that people suggest above will work that much better.