Hack was done long time ago but I didn`t have the time to test.
After I changed oil due to fuel contamination, I managed to idle the car with the patch at 3 bar with the vacuum disconnected. It runned real smooth and the afr was really stable. I put an aeromotive fuel pressure regulator and have plans to bump the pressure to 4 bar if the pump can handle it. It does make some unusual wine when the car is turned off.
Initial version is only for auto bin. It may need some tweaking. I hope the PCM is fast enough to handle the dynamic fuel flow calculations. Otherwise I will have to move the patch at different locations and test untill sufficient results are obtained.
I had really hard time interpolating injector data. At least I have the tables done for the ls1 injectors with part number #???#, I will dig it later.

I did research ls1 fuel system. 97 ls1 corvettes have a fuel pressure regulator on rail at 4 bar, no vacuum applied. Later years they moved it to fuel filter. Ls1 f-bodies have fuel pressure regulator in tank and the return line is close to the tank with a t-union.
So ls1 is indeed a return system. The return line is not on the rail though.
It is missing the vacuum reference at the regulator and the PCM calculates the dynamic fuel flow based on manifold vacuum. If you have the correct calibration data it is much more accurate and predictable.