I'm guessing others may have tried this before but thought I would share just in case.
I used 6 harbor freight magnets to hold the headliner in place so that I could get in the correct position before spraying the glue on. I think 8 magnets would have been better.
Once I had the liner where I wanted it, I moved all 6 magnets to 1 side of liner and sprayed the glue on half of the liner and used a painter roller and my hand to smooth it out. I then moved the magnets to the other side and repeated the process.
An added benefit was that after the glue set, I was able to slide the magnets across the linter without removing them. This allowed be to use them like a squeegee and get any sagging areas smoothed out.
Be sure to get the magnets that have a 95lb working load rating as they stick perfect to the underside of the roof. 66mm Round Magnet (harborfreight.com)
Thanks,
John