If you can't/don't want to boost, I was able to do this legit (and also unlocked Job Skills) by doing the following:
Play a game in wanted and attract the attention of your pursuer. Once the chase has started, start chasing your own target so that you're effectively chasing and being chased at the same time.
Catch up with your target and assassinate him/her - during the animation, try to determine how far behind your pursuer is. Quickly deploy your smoke bomb at close range to halt your pursuer, then press B to knock them out. This instantly counts as an escape.
I appreciate it may take a fair amount of luck to get yourself into this situation, but seeing as most of the guides here are geared towards boosting (credit to the guys who have provided good guides here already), I thought I'd put this out here so people know what to do if they have the opportunity.