The best way is probably to walk from 'Montpelier' (a.k.a. The Watersplash) on the Druidale Road. There is a footpath heading of in the direction of Snaefell. It will be quite a hike though. I'll dig out a map and have a look. Alternatively there might be a way around the reservoir from the car park. But, I'm not sure if you are able to cross the bridge at the top of the valley below the Tholt-y-Will to The Bungalow Road.