Oh, I thought that this
was short rushing.

OK, well if short-rushing isn't what I thought, the following is an example of what I meant:
Eg. If I have a town producing 10spt and I'm building knights there. I let it start on the knight but after 1 turn I temporarily switch to a musket to rush an additional 50 shields and then switch back to a knight to let it complete the build on the second turn. This costs 200g and two turns. If I have less money available (or if the sims don't work out quite so neatly), I leave the build for a few turns. I don't rush the first part because you pay double and all those 40 golds add up and I also try to use of many of the shields as possible from the final turn's production.
Has this technique got a name?