I don't think there is any magic bullet for this one.  Closest thing to one for me has been to say,  "When was the last time your advisor had time to sit down with you to review/rebalance/reallocate you funds?"

what works well for me is

Well thats great, and the reason for the call is not to steal you away from your current advisor because me and you both know that would be virtually impossible but I was simply calling today to  complement what your current advisor is currently doing.  If I can show you how to increase your returns all while reducing your risk and minimizing your taxes do you think this would be valuable to you?

This will get an instead lead almost 50% of the time.

"What did he do for you in 2008?" (btw that's a joke)

Ricky is pretty spot on.  I wouldn't put the other advisor down, because it's probably someone's friend or uncle or something.  Congratulate them on working with someone, then ask what they have been working on or have set up.  Usually they have no clue, and then you have a hot button.   If they do know they will list off a variety of things.  Retirement accounts- tax free?  guaranteed income? Safety of principle?   After you find a hot button give them your value pitch.    It is a tough objection but not impossible.