Hosing the ice off is a great idea. Be careful not to hose in areas where there is roof damage. Water damage is expensive to fix, I know, I'm homeless because a pipe broke.
Running a rope to the other side to climb off, is also good.
The two ideas that just suck are just drag it off, this will surely cause more damage, and just start cutting from the base, bad, bad idea.
Please notice the importance of removing as much load to the roof as possible BEFORE you start working, then as you remove brush it will start to float. Lift with a rope, support with beams or both. If you don't, the load on the roof will increase as you remove brush because all the weight will be concentrated in one spot. The most difficult part is when you get down to the the edge of the roof.
By lifting first, if something goes wrong or doesn't work, there is no damage done. If you wait until the brush is removed, then start lifting and something goes wrong, a short drop of the trunk could go right through the roof.