There might be several approaches you could try. No guarantees whatsoever, and I didn't try any of those. Still mentioning them, so you can investigate for yourself. Note further that these solutions will require root access on your device.
First, there's an app called SwitchMe, which already was available before the multi-user feature was released with Android 4.2. SwitchMe works with Android 2.1 and higher.
Second, our friends at XDA have a thread on Porting Multi Users JB to ICS (but it seems that approach died before producing a workable solution).