with any dog behavor your likely not to "stop" the behavor but you should be able to at least control it.

The first line of attack so be to inform those new to the dog that he/she likes to give kisses.

if its getting to be excessive (ie your sitting in the living room trying to entertain your friends) you should be able to give a comand to have them stop. (its not likely to work permantly but they should at least leave it a long for a bit)