Just use a pencil. It sounded silly the first time I heard it, but it worx. Use HB mechanical lead or your standard #2 wooden pencil, but make sure it's sharp, and be careful not to connect adjacent bridges. Also, use a magnifying glass to check for crossovers as you go along. Some say you will need to reapply the marks every now and then, but mine's been working unlocked for about 4 months now... no probs at all, except that I want that gig badly.. hehe
Other ideas?
Window defogger repair kit. You'll find more ppl doing either the pencil or WDR trick than using conductive pen, as it's more practical.
Proof?
Unlocked D750 @ 927 (9 X 103)
Stable... no pencil reapplications since I first unlocked it.
K-Lined4Lyf