Multisim has an MCU Module as an optional add on. This module right now only supports the 8051 and PIC16F84 microcontrollers. You can not at this time add any other controllers to it. You can not simulate a microcontroller or microprocessor with any spice based programs that I am aware of other than what I mention previously with the Multisim MCU Module. Thes IC's require programs to entered into them and their is no way to do that with spice based simulators that I am aware of.
Multisim's MCU Module is the only platform in any simulator that allows you to create a program for the processors it supports and create a circuit that simulates with the microcontroller as a functional part of the system. Otherwise, I do not believe what you are wanting is possible.
Sorry to have to tell you this, but this is what I know. It may save you a ton of headaches trying to do something that won't work.