Tripod Collar for Macro Rig

I currently am shooting macro at 7.5x with my T3i connected to a full set of cheap Fotodiox extension tubes (Like these), a 55-250 IS II at 250mm, f/11 and MFD with a 50mm f/1.8 reversed set to f/8. The problem is that I cannot mount this setup on my macro rails and tripod because it is so front heavy. The balance point seems to be on the extension tubes. My question being does anyone know if there is a tripod collar that is a fairly close fit to the size of the extension tubes so I can mount the lens with better balance?

A Manfrotto Lens Support bracket might work. It's relatively adjustable.

It will be a real pain in the arse to change the aperture with those fully manual tubes. If it were me, I'd spend the money for one of the better sets of extension tubes with electronic connections. At least these cheapies with the plastic bayonet mounts, though for just a little more better ones with metal bayonets are available. The ones linked are ProOptic (Adorama's house brand), but are made by Zeikos and sell under that name, Bower, Vivitar and probably a dozen other brand names, too. They are all the same. You just need to be sure to get the later version with the little white square box on them, that indicates they are compatible with your EF-S lens. (Earlier ones were EF only.)

Changing aperture isn't a huge problem with this setup as I only have to do it when I put the rig together. I rarely see the need for an aperture different than f/11 on the 55-250mm as it gives acceptable depth of field but doesn't hit the point where diffraction ruins the image. The 50mm is only at f/8 to stop chromatic aberration which was horrific before I though to stop it down. The setup works well in is current configuration apart from trying to mount it to rails.
The one part of the story I forgot to mention is that I am a nearly broke college student. If I can solve this problem for under $20 it would be great as I love the setup otherwise. When I use it with a homemade bracket (Think piece of wood with holes for 1/4" screws for the camera and flash) and YN-560EX flash, the setup is awesome, just hard to get in focus handheld, hence the macro rails.