You can use generic automotive worm-screw hose clamps, on any cage where a VO would fit. Low profile, stainless, fits virtually any diameter of frame tubes, even oval or some moderately "aero" shapes. Definitely put tape under them though, rough on paint.
Someone sold those with with an M5 screw welded on. I thought that was clever. All the above advantage plus works with the cages that don't have TA-style tabs where the VO type clamp will work. Maybe even still available, but that would require someone knowing what the heck I'm talking about. Sorry no pics.
Also maybe hard to find but Zefal made some H2O clamps called "Gizmo":
Never tried 'em, can't say how strong or rigid they are, but they should be easy on paint.
Mark B