Just to say I was at EZE this morning and signs to "Pasajeros en conexión" were easily spotted throughout the arrivals hall before reaching border control. Following these signs leads to a stairway which itself ends in a security check.

EZE was my final destination so I didn't try it, but it all seemed quite organised. There was ground staff at the jetway helping connecting passengers who got off my flight, but I don't know whether this is usual stuff or it's BA that goes the extra mile.