prasanta_g,
You can make gm vary with R using a standard constant-gm biasing circuit. This will help to account for variations in R by making gm vary inversely with R.
However, this won't compensate for variations in the MOSFET (such as tox and doping variations).
You can scheme up a way to trim R to account for the MOSFET's variations if it's really so important. However, usually it isn't important enough to do this, so we simply design the circuit with generous margin so that regardless of how much the zero moves around due to MOSFET variation (which might be ±30% or so), the circuit still functions as planned.