multivariable Root Locus plots

I would like to get an Rlocus plot of a transfer function containing multiple variable.

For the sake of the example we can just use any transfer function with a gain of "T" in the numerator and lets say some other variable in the denominator 'R'

If i simply do this in a loop i will only get certain combinations of T and R For example if i increment T and R both up one value per loop revolution.

How might i go about this for all combinations of T and R?

I know this is semi vague and its done intentionally. I don't want to go over specific examples here i just want to get some ideas.