I never have that problem with the riffle force these days. When I do it it's more about the converstion between me and the spectator which goes "Tell Me when to stop" *brief pause* "Stop!". The cards are merely there to give meaning to why you've asked them to say stop. They feel like it was a free choice of card but in actual fact the deck of cards had very little to do with any of it.
If you feel like someone is trying to take the p*ss with you then try waiting for them to say stop ridiculously late and riffle off the rest of the deck as they say it. Then say "do it while I'm still going down the deck if you don't mind, it doesn't work when there's no cards left." Failing that go with the exact card they want you to stop at and let them have it...and do a pick a card trick that needs no set-up and no force. If you don't know one of these you really shouldn't be attempting card magic.


