Aluminium != Tin
There is something you could try doing, rather than having a broadcast you could try narrowing it down into a receptive/broadcast cone.
There was an ad-hoc method rigged up for people fishing for wifi connections originally, since there setup's didn't have an old fashion Citizen Band (CB) squelch dial, they would utilise apparatus like old pringles tubes to fit their antenna's in.
Pringle's tubes were used because of their internal metallic coating and with the right jury rigging it allowed the tube to be pointed in a direction to identify the source of the wifi reception.
I think you could do an adaption on this and create a way for your router to broadcast in the direction that you point it. Of course it would then require either two people to trial and Error it into the right position, or you'd have to do some sophisticated Mathematics to work out the relevant angles on your own.
(If you are interested in making such a device, I would suggest looking into the 2600 material)