Hi ploffer, welcome to the forum. Great ideas there.
However we really try to keep talk of steath recording, stealthly around this public forum. Otherwise we may end up loosing those opportunities. Could I ask you to please delete the post above.. or modify it to eliminate all the undercover details? Thanks! and I mean no offence to you, I like your thinking.
If possible, try to keep discussion of these techiques restricted to private messages to other members in good standing, using the PM icon under their avatar.