I used paint/adhesive remover. The 15-20 minute kind. Put a coat on there, let it do it's work. Wiped it off, got a lot off. But not all. Contact cement leaves a lot behind after the adhesive part is broken down.
I used a scotch brite pad to rub off the old contact cement. Worked wonderfully. Took the old glue off, not the wood. Those pads are ideal as they don't "load up" like sandpaper does rendering it useless after a minute. Also, the scotch pads grab more.
I kid you not, the subrail was literally brand new again. As if the wood was freshly cut that day. No damage whatsoever from scraping, sanding or other methods. There was no indication whatsoever that a cushion had ever been on it before. Perfection.
I only had a problem with one cushion that took some wood with it. Had to fill small parts of the subrail with Bondo. But that had nothing to do with the remover or this method.
Only downside is, highly recommended to cover the rails. A drop of that stuff will take off the finish.