Thanks now I understand clearly what you mean.
The answer is donot look for that, as you cannot get it.
Other thing the constant-gm bias is to generate a biasing current. And this biasing current would vary by 100% (+ and -). Rest assured across PVT.
We take the current generated by this to all the other corners of the chip where we need the current and generate a local biasing there.
And your aim is to get the current mirrored.