Leeoof, you could always use track(s) with an insulated outside rail as an activation device. I have done this for a modern Lionel Double Signal Bridge, although when the red light goes on as it should, the green light still flickers.
This is shown in the video below:
Other methods, like the one recommended by Gunrunner John, would eliminate the flickering.
Incidentally, I'm fine with the Postwar weight activation device provided it's located in a place that is accessible. I have a Postwar gantry signal bridge which has been very reliable using the weight bearing device:
Arnold