I did not completely understand your question but I am going to go out on a limb and try to guess it.
So you had a transistor, and you found that your Rollett stability factor is less than 1. And you want to know what to do?
K>1 means unconditionally stable but K<1 does not automatically imply your amplifier is going to be unstable. It depends on your load and source impedance. If your load impedance is fixed, you can draw the load stability circle and see if your amplifier is going to be unstable for the load impedance that you are targeting. If no, then you should be fine.
But if yes, then the only thing you can do it place a series resistor with the gate of your device to reduce the gain and see at what point your load lies outside your load (in)stability circle.