It's going to take some bracing first, for sure. I'd suggest using metal. A 1" wide piece of 1/8" strap bent to the right contour and tacked on the hands might work good.... Then it's a matter of ding and ping, shrink the roof so it fits the contour of the braces correctly. Word of caution, the more you work the roof panel with hammer and dolly, the more it will stretch.....so be careful of how you work it...

I know you probably don't want to hear it again, but IMO the best plan would be to remove the roof panel and the wood strips and start over with a station wagon or van roof with the reinforcement beads already stamped in it....