Well, that isn't an easy question. I haven't come across any definitive answer to that specific action so consider this as just my opinion. Rule 42 "Propulsion" is a tough one to enforce, and even the Senior Judges are unsure in some cases. SAYRA had Pat Healey (who is an excellent speaker, by the way) come give a seminar on propulsion to the judges at the last annual meeting. He went through the different ways that people can move a boat around and gave practical tips on how to spot it. Pat also went over the ISAF interpretations of Rule 42 (available at: http://www.sailing.org/rrs2005/42interpretations2005.pdf).

One of those interpretations is:
Given that a dragging a leg in the water isn't one of the permitted actions, I'd have to say that means you can't stick your foot in any more than you could stick a paddle in.

I doubt that anyone would protest you for dragging a leg, and a protest committee would have to be pretty sure of itself to penalize you for it. Nevertheless, I'd suggest you don't. I prefer to tell people how to follow the rules - not how to skirt them.

That said, one of the permitted actions is Rule 42.3(e): If you want to slow down at a mark, you could legally steer back and forth (think of it as sculling to reduce speed). Dragging your rudders is a very effective way of slowing down without dragging a leg.

You might need to show a protest committee rules 42.2(d) "Prohibited Actions" and 42.3(e) "Exceptions" if someone accuses you of sculling.

Well, that's my opinion anyway. I hope it helps.

Regards,
Eric