Sorry for taking so long to get back to this thread.
I personally don't think either approach (intentional foul "nudge" vs. 2 or 3 rail kick) is objectively wrong. For me it came down to a philosophical decision. I'm facing two possibilities, and either one has a definite chance of losing the game for me. With the kick, I could hang the 9 and sell out an easy combo or carom. With the "nudge", I could roll either ball 1/2" the wrong way, and sell out a combo, carom, or very easy run-out. The guy I was playing against is only a little better than me, but with the balls in their current positions, adjusted so the 5 is makeable, any good player is out from here.
So there's a very clear and present downside to either choice, so I looked at the upsides. The upside of the nudge is I could leave it so he has to play safe, and then have to win a safety battle for the match against a better safety player than myself, with him getting to play the first safe with ball in hand. The upside of the kick is I make the 9 and I win right there on the spot.
I started to try to factor percentages in to the decision, but I realized I was dividing by zero on one side of the equation. I thought of something a lot of people say when deciding whether to call a river bet playing hold 'em: "I'm just trying to think of a hand you could have that I could beat." When someone says this, it always means they realize they have to fold. For the intentional foul, I was trying to think of a way it could play out where I win. I really didn't see one, so I folded that option, and took my only other choice.
-Andrew