Originally Posted by MichaelW
Hook and elastic systems are not the best mounting system, they can bounce off with a bump. Modern panniers use a quick-release locking hook at the top and an anti-sway hook that fits inside the vertical rack stays.
Arkel makes "modern" panniers that utilize a hook-elastic system that are tried and true. They have a locking mechanism that prevents them from bouncing off. That said, I do prefer the quick-release aspect of mounting systems such as Ortlieb's. But many hook-elastic systems work just fine.
As for the original question: My rack is like yours in that it lacks the "hooked" stay ends. I have found though that my Arkel hooks still hold on to the stay ends, no problem. Have you tried it yet? If your pannier allows, adjust the elastic cords so that, when hooked, the tension is drawn more diagonally (vs. vertically) to keep the hook more secure. That is, if you attach the hook to the rear rack stay, adjust the elastics so it pulls toward the front (hard to explain - let me know if you need clafication). Not all hook-elastic panniers have this adjustability, but Arkel does.
I've been commuting about 38 mi round trip for 6 months and the pannier has yet to come loose. In fact, sometimes I forget to "lock" it and it never bounces off (of course, this is all on-road).