Originally Posted by
Homebrew01
You could also put skinnier tires without knobbies on your current bike and pump them to full pressure. They won't be as fast as road bike wheels, but for a single event, it's a cheap way to gain some improvement.
+ 1.
Assuming this is an occassional thing and the OP doesn't want to sink a lot of money into it, skinny slick tires will make a big difference on the rolling resistence side of things.
And some cheap clip on aero bars will help the aerodynamics a lot.
I bet you can find an old pair on Ebay or Craig's list for $25 or less.