If I had that fixture I would look it over very carefully to see where it would be safe to drill into the fixture. Watch out for the ballast, if it is inside the housing somewhere. You might be able to drill into the ends or the top of the fixture. Ideally you would partly disassemble the fixture so you could put nuts and washers on the inside of the fixture, and install eye bolts for chains or cables to suspend it by. If you can't use nuts and washers I would use sheet metal type eye bolts and be even more careful when screwing them in, limiting them to the ends of the fixture, not the top.