My current attachment point (Crotch strap D-ring is about 4" below my waist strap, to allow me to reach the points. The buttplates put the rails basically between my legs & too far down for me to effectively reach. I do have a set of the thick Rubber O-rings that can be used for sliding rings on the waist band.
There's some very effective approaches for diving aluminum cylinders. Trying to bastardize aluminum cylinders to behave like steel cylinders (adding cylinder weights) is
not one of them. Steel and aluminum really do benefit from different approaches.
But creating 'mock steel tanks' is what a lot of divers with more steel, than aluminum, cylinder experience will advise. Stick with what you know, I guess. But it's not optimum, by any stretch of the imagination. It can, however, be more convenient if you're diving steels at home most of the time...and only doing brief trips to warmer climes where aluminium is norm.
If you're constricted in rear attachment options, then do look into loop bungees. These create a useful rotation effect of aluminum cylinders, torquing them into the side of the torso. This also means that your attachment points, front and back, don't need to be spaced so far apart.
Depending on your waistline, you could probably get away with putting a simple D-ring at the rear, where the BCD is tightened down on the waist strap. And another D-ring forward on the hips.
Personally, I find switching D-rings much easier and less cumbersome than a sliding D-ring approach. Rubber O-rings, such as those which come with XDeep sidemount rigs, aren't that slick to manipulate.
The rubber O-rings do, however, make a great attachment point on the
shoulder straps through which to route your (sliding) loop bungees.
