I suspect that if there is a benefit, it will be pretty minimal. There are potential costs to double clutching. Eg:
- you could spend more time out of gear.
- increased engine revolutions
- more focus on double clutching, means that you as the driver can't focus on other things, which may have more effect on your hypermiling.
Its probably all a wash. Until you are already an expert hypermiling driver, I doubt a slight reduction in wear and tear on your gearbox will make up for what benefits you could get from hypermiling well. I would spend the effort there