Sorry. I didn't mean to put you and your method down. But I don't see how your sex is of importance in this discussion :P
You live half the world away and I'm probably twice as old as you are (I don't imply you implied that, I just mentioned it, because sometimes I think I'm funny)
My brain hurts.
If it's important where they put the card and the card above or below are not prepared in anyway, why is it important where you put it?
I'm aiming blind here, but maybe there's a pull of some kind :P
Though I do not see where it would go and more importantly how the card comes into the deck again :P
Except there's a flash of one card, when you spread the face-up top half, but I can't see what card it is nor can I think of a sleight to get this card to the top half, meh.
Very fair of you to give it another week, but unless someone else posts some new guesses I don't think I will come up with anything new.
I can't see any sleights and I basically mentioned all the gimmicks that would make this effect non-impromptu and still work with any deck...