If I had Thule bars and didn't want any other kind of rack system (like a basket), I think I'd just drill through the bars. I'd put a fairly long bolt in (from the bottom, up). Then I'd thread a nut on from the top to keep the bolt from going anywhere. Maybe use a fat washer on top of the nut and then throw the Hi Lift up there. Put another fat washer and a nut on top to secure it all. If you want, you could even drill through a bolt and install a small lock. Make sense?