In reply to SomeClimbingGuy: This is the smallest I've seen but to be honest it won't do much more than keep your bum clean on sit starts.
http://www.gooutdoors.co.uk/wingman-p195520?gclid=CPDwlarenLgCFfMbtAodcVcAz...
You may still get buffetted around on the bike with it on.
There are pads that use air but they are designed to be filled once then left full (it takes a while to set them up) and they're massive.
I'd either go to popular venues where you can join in with others or take shunting gear in a sac.
Or go soloing.