I’ve got a little bit of thin closed cell foam with a peel and stick back that might work if you find that the switch is such that it can be applied to it.
PM if that’s the case. A better alternative might be the very sticky wrap that HVAC service people use to wrap refrigerant lines to prevent condensation. It’s very sticky and molds to any shape and stays in place well. I bet they would just give you an inch or two of it.
I'd be really careful putting anything on the switch. Those things have REALLY close tolerances. The slightest press on the brake pedal will light up the brake lights. Anything you put on the switch might either a) keep the brake lights on all the time or b) keep the brake lights from coming on as soon as they should.