Put heat packs in grid format along the sheet.
Attach sring to the break point of heat packs
Once snow is on roof pull strings to activate the heat packs
Once enough snow has melted pull off the clear sheet.
I live with a moderately steep driveway facing onto a moderately steep and short road, with me having to go uphill to get out of it (dead end otherwise), and I have to admit I've entertained the idea of melting my driveway off in a similar manner, but only because I'm a bit darkly amused by icing the entire rest of the road so nobody below me can get out, even with four wheel drive. I suspect local law enforcement would find a reason to fine me, though, and they'd be very right.