Hi there,
There are programs that help you to do this but they are a bit expensive, and also require many measurements to get it right. I doubt you would want to go through all that.
It does help to know the part well, in which case sometimes you can sit down and write a spice file yourself that models what you really need and maybe not every single aspect of the device. A very simple example of this would be to model a transistor as a perfect switch with some series resistance, which would work in certain restricted analysis scenarios.