[quote=Corsair]
If I can be a bit of a pedant, only the secret-keeper of the Fidelius Charm can pass on the secret, it doesn't work if other people do it. That's why they had to give Harry a note personally written by Dumbledore so he could find Grimmauld Place.
[/quote]

Oops. I knew that to be passed on verbally or written, but thought that it could be visually passed on by anyone who knew the secret - I had overlooked the fact that Harry, Ron, and Hermione had become Secret Keepers to Grimmauld Place when Dumbledore died, making it possible to do so.

@Doused, at this point if we go the careless inductee route, the inductee (Tanya) would have to be exceptionally careless, because the only option I can think of is something along the lines of:
[i]Luther run up to her when he sees her appear, drops his wand/hand to her to show that he won't attack her (although since Luther excels at Muggle combat, he could just as easily attack her without a wand, not that he would in this case :P), and persuades her to talk to him. The Ashes, looking around for where that pesky Tanya has gone to, see this and run to us, assuming that I'm either attacking her or something, or she is passing on information, either event of course being very bad for them. When they arrive they decide to listen since I'm already disarmed, etc etc.[/i]

Of course, if we don't go the careless inductee route, I could just stand at the edge of the Charm with my hands up, and wait/hope for someone to come do something about it. But where's the fun in that? (Assuming they don't just let him sit there, until he is forced to leave either 1. to eat/etc or 2. so the other Death Eaters don't get suspicious of his absence)