It seems that Thanko has managed to come up with a solution for those problems with their water-cooling cushion. How it works is through the use of a water pump that will pump water around the cushion, keeping your back and bottom cool during a particularly hot ride home. It claims to be able to keep you cool for around 6-8 hours and dropping temperatures from 55-60 ℃ to 28 ℃ within 5 seconds.
It can be powered by a cigarette lighter adapter found in cars or with an AC adapter which means that its use is not just limited to cars but also to home and anywhere with an AC adapter. It will cost ¥14,800 which roughly converts to $191 and will be available from Thanko’s website.