How do you cap the generated frames?

For my understanding and testing, Nvidia control panel or 3rd party apps like RTSS or special-k ONLY caps the real fps.

I'm on a 144hz with g-sync and the games stutter a lot with LS when I reach 144 fps, anything under works like a charm.

I can cap the real frames to 71, LS generates more 71 making 142 with works fine. But I want my gpu to generate whatever frames it can, like 100 and the LS the rest.

So, is there any way to cap the sum of the REAL and GENERATED frames?