In the past I have acquired these fasteners with a clear,
thumbtack-sized head on them and a sharp corkscrew type shank which was
intended for sagging headliners, came about 15 in a package, they never
came loose and didn't even look that bad. The edges of the head were
splined so you could easily screw them in with your fingers, took about
5 minutes to do, worked on an otherwise pretty decent 82 Regal I once
had, looked good enough to leave it at that.
Don't know if they're available anymore as I haven't seen them in
awhile, but haven't looked for them either.
But if the vehicle is a really nice one the other suggestions might be
better for you.