In Psych's final episode, it was established, beyond any doubt, that the universes of Monk and Psych are canonically the same universe.  For anyone who watched Monk, one of the primary bad guys of that series was Dale J. Biederbeck III aka "Dale the Whale ".  Dale knows everything about everyone.  Even from his prison cell, he'd know all about Shawn Spencer.  HOW the two of them interact would totally be up to the writer.  Maybe Dale sends for Shawn to solve a mystery - or possibly to share information on something?  Dale always has an underhanded scheme to benefit himself so nothing he does is without ulterior motive.  Good luck!!