Power button - replacing foam spacers?

When disassembling my moto x to repair the display assembly, the small bits of foam that should be glued to either side of the inside of the power button fell off and were lost (I guess the glue had worn off). These spacers seem to have been compressible and to act somewhat like "springs" to allow the proper functioning of the power button.

I am wondering if anyone has a suggestion for a good (ideally readily available) material to replace the missing spacers? I have a temporary fix using a little foam cut from the inside of the old display and held in place with a dab of "sticky tack". It works, but not very well (takes a lot of force to turn on/off). I also tried cutting small pieces of rubber band, couldn't get that to work.

Any help greatly appreciated!

Thanks