How to deactivate hyper memory

[Motam]

Hi,
I am looking for a way to (experimentally) deactivate hyper memory for my HD5850. I have a Phenom II X3 720 with 8GB ram and the GPU has 1GB on a Win8 install.
When looking at the properties window of my GPU it states that it has 1GB internal mem and 3.8GB additional (theoretically) shared memory.
To be clear, I am not worried about running out of RAM on the system. I trust Win8 enough to free the RAM when it is needed.
What I am more worried about is framerate losses due to shared mem usage (mem bandwidth for RAM is a few GB/s, GPU RAM is in the vicinity of 100-120GB/s). I am aware, that the shared system memory is only used in case the 1GB is exceeded but in modern games, this is quite possible.
I would like to disable the shared mem to see if I get fps increases in some games (notably Rift which is chronically underoptimized but also on some other games).
Does someone know a way on how to disable it? Most posts I found stated it would not be possible and some pointed to ATI Tray Tool (which does not run on Win8).
Any solutions?

Cheers,

Motam

[Bad 💀 Motha]

Shared GPU VRAM is an OS thing; u can't change that, ever.

Ignore the OS statements in regards to Shared GPU VRAM; it is a non-issue whenever u are only using Dedicated GPUs.