When I ran an electrical wire from my garage to my back patio (to feed my tiki bar and kegerator), I got three 8 foot 2 x 8's and used them in the attic to have something to safely move along as I worked my way back - continually moving boards in front of me and resting along the rafters. It's slow, but pretty safe with regards to protecting your roof.
I have stairs in my garage to get to the attic, and an opening in my rear bedroom. Once I had pulled the wire and fed it where I needed it, I exited via my rear bedroom, along with all my tools. The boards remain in my attic for the next time I need to go up there (hopefully never
).
Make sure you wear long pants and long sleeved shirts - the insulation can cause a lot of itching!