I think a good question would be what kind of motorcycle? Crotch rocket, would probably need a side mount almost like how guns can be mounted to a ATV/4wheeler. If you have a big fucking cruiser your best bet would be either a tow behind, or trailer hitch mount like you can find on the back of some cars/trucks.
I have tried putting the snowboard on a backpack but I noticed its not very stable and its very wide. I'm worried about the wind resistance the speed limit is 50, would there be a significant amount of wind drag? I'm actually not going up the mountain but plan on riding it to a tram that takes you to the top. I might just go with the backpack idea and just hold up traffic. I hope my snowpants don't melt on the exhaust haha. Its a CBR BTW.