How can a root locus plot of a feedback loop be created when the controller varies with s?

I understand how to create locus plots of feedback loops where the gain is just equal to k. But what if the controller is more complex, such as K(s)= 4k + ks for example? For an open loop transfer function of, as an example, 4k+ks/s^2 +..., I am unable to plot the locus without an error appearing that says k is not defined. Any help would be greatly appreciated. Thanks!!