teaching an "off" command

You guys were so helpful last week with getting my dog to respond to my calls (she now comes enthusiastically every time!) than I’m coming to you with my next obedience question. 

Oreo is a Boston, and while we love having her sit in our laps, she can’t seem to do it without licking our faces incessantly.  I know it’s a sign of affection, so I don’t so much want to stop that as action of lunging up to start licking.  I’ve tried redirecting her attention, but it’s short lived if it works at all.  She is SO focused on giving kisses, than nothing short of tossing her on the ground works.  So, I guess my question is how best to teach her an “off” command for something like that?