I was going to post this one with a plea for help, then I figured out the approach while I was typing the title. I stared at this one for half an hour and found nothing, but the light goes off when I come here. Gee but this forum is so helpful. I got the answer before I posted! You guys are awesome.
Ok, so here's the puzzle in it's blank state:
I'll post the puzzle at the bottleneck in the first reply to this post.