The technology to flex a large surface into an accurate optical surface does exist. It is used on the Keck telescope but it requires that the glass segments be made of Zerodur ( ultra low expansion glass). micro actuators to flex the glass at multiple positions, a complex structural model of the whole system that predicts the flexing of the complete structure, a laser alignment system, with active feed back and a computer system to control all of it.
There are many very smart people in this world and if there were a simpler ways of doing it, someone would done it by now. So when an solution to a problem looks to be simple and no one has done it yet, what that means is that the problem is much more complex then one thinks and one needs to do more research to truly understand the problem.