Playing with a pickup partner, I agree to Standard American, plus Cappelletti and some other gadgets she insists on. The way I see it, who cares what you play with pickup partners? Better to just keep it simple and not stress about conventions - once you've talked about it, you won't be lucky enough for it to come up anyway.
So lo and behold, I find myself with a good one-suiter after the opponents open 1NT. Dutifully I bid 2C (an artificial relay to 2D). Partner passed the relay and we wound up in a horrible spot for some horrible result. Confused, I ask her if we are playing Cappelletti. "Yes," she replied, "but I thought you forgot."