Back in my motorcycle riding days I’d wear a beanie under my helmet and heavy gloves. Both were powered with D-cell batteries (it was a LONG time ago) and were basically little electric blankets. Couple those with some long Johns and a nice jacket and you’re set!
A quick check on Amazon shows similar devices running on much smaller batteries. They seem to be tailored to the ski and snow-board crowd.
Keeping the fuel tonneau closed on the passenger side will help as well...if nothing else it’ll keep the wind from whipping around you and may even hold in some heat.
I’d check the sports stores and see what is out there for the heated caps and gloves.