We did that in 99 with fake mig-29s, the body was made of sheet metal so it would react to radar and the engines would be metal barrels in which they would burn wood to simulate the heat of the engines. Enough to say that the supply couldn't keep up with the demands and almost all of the decoys were destroyed while none of the real planes were hit.
We also did that with tanks in Kosovo, it worked so well that NATO claimed 181 tanks, 317 armored transporters, 857 cannons and 600 militray vehicles were destroyed. When they visited the sites of "destruction" with the press it's fair to say they were pretty embarrassed. When the Serbian army was pulling out of Kosovo they had convoys with 250 tanks, 250 armored transporters and 600 cannons, which was pretty much everything that was deployed there.
We should have sent the brits a couple of those fake tanks as souvenirs.