I've never heard of longer aftermarket roof rails.
The roof is sheet metal welded on to cross braces. You'll likely need to find the next cross brace to set the next hole or you'll likely end up denting your roof with any like of weight load. Actually drilling the hole is the same as drilling any other sheet metal but you'll need to partially or fully drop the head liner so you have space to work. In order to drop the headliner you'll need to remove the grab handles as well as the A, B, C, & D interior pillar panels. The B,C & D interior pillar panels won't come out without removing the sill plate panels. I think you'll find it easier to partially drop the head liner instead of removing it completely. Once you have the head liner dropped you can drill your new holes and use a thread setter so you have something to screw into. This is a freaking cool tool for just the thing. Without this you'd probably have to try and weld a nut. It's a lotta work. Is the roof rack worth it? Got any pics? I wonder if you'd be better off selling it and then buying a rack that fits.
Link to Marson Thread Setter on Amazon $89 Shipped