25mph average is FAST. At that speed, wind resistance completely dominates. Drag is a function of speed squared, so a marginal imcrease in speed causes a big increase in drag. Eg if you increase speed by 10% drag goes up by 20%. To increase your performance by 20% is a huge jump if you are already near your maximum. I would say impossible.

The only real way to get significantly faster is go aero. Install aero bars and tuck down for an hour.