Reddit mentions of 6061 Aluminum Angle, Unpolished (Mill) Finish, Extruded, T6 Temper, ASTM B308/AMS-QQ-A 200/8, Equal Leg Length, Rounded Corners, 1" Leg Lengths, 1/8" Wall Thickness, 72" Length

I'm not suggesting you add a secondary support. Rather, just a piece of aluminum angle bar mounted on the front support, at the same height as the rear support. This will allow the front of the GPU's PCI I/O shield to rest against a solid surface, effectively holding up the attached PCB even if it can't rest on a rear support. In fact, you could probably reduce your costs if you used this same angle-bar for the top portion of the front-support as well. It would allow you to thread the mounting points just the same as using tubing, but would eliminate any issues with DVI ports placed within 1 inch of the top of the PCI I/O shield (which would otherwise prevent you from being able to mount the PCI I/O shield flush against the tubing). It will also eliminate the issue someone else mentioned regarding obstruction of the I/O shield vents on reference GPUs that exhaust out the I/O shield. Lastly, using the angle bar in the secondary, lower position on the front support structure allows for the addition of ASIC-supporting-sheets for future expansion, effectively making your chassis more relevant because of its upgradability (another made up word).

If I've still failed to explain myself clearly, just try this: Attach a second, horizontal cross-bar to the front support structure at the same height as the rear support's horizontal bar. This sorts out support issues for short cards, and adds a level mounting surface for ASIC-supporting acrylic sheets. And if that front-support horizontal bar is aluminum angle rather than tubing, it should cost less. And if the top horizontal bar of the front support is also aluminum angle rather than tubing, you've further reduced your costs, and eliminated any compatibility issues with DVI ports or exhaust vents.