Oh, he didn't suggest it for the film. They overheard him use it in a motherfucking conversation.
The screenwriters were so overwhelmed with the line's mind-melting profundity that they shit where they stood, before rushing off to add it to the script. In the final version of the film, Snipes utters the line just moments before kicking a villain in a special way that causes the villain to explode. The fact that some motherfuckers are, in fact, always trying to ice skate uphill was the last piece of wisdom the antagonist carried into the afterlife (The writers don't mention if Snipes delivered an exploding kick to punctuate the real-world conversation they overheard, but their silence on the subject suggests he probably did.).