If you enable the movement option (Num Pad 1 in the trainer) then tell a worker to construct a route or a mine or any improvement they do it immediately. It doesn't even take a full turn. You tell it build a farm, and it does, then it can build 10 more in the same turn. As many as you want it to.
Not exactly what you were asking, but it sure does make it easy to build roads and railroad tracks
Hmmm...well kind of...that works, but the problem is that it requires you to build all the improvements by hand.