most ski insurances will have some form of "no snow" insurance included. Not much though and there are stipulations. If you wanted something more detailed you would have to specify and the insurance would be weighted accordingly.
we were in Boro Jan 08, skiing cond was poor unless you went right up top. We took some pics of the bare nursery slopes and managed to claim 2 days (non)skiing back.
Off to Tignes in Jann 09, loads of snow. Get in there