I think short poprivets will work. You will need to take an old rivet with you and find a poprivet at the hardware store that is the same size and length.
You can easily reach the rail if you remove the rain gutter (which means you may need to remove tha panel), or you can have a good shop do the repair for you. I haven't gotten my roof panel back in quite properly yet, but I didn't try too hard -- I have to take it back off later to paint the edge and replace some more parts, too. It isn't taped to the top of the car anymore, which is what I was really after.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!