What about leaving it at left luggage? You will have to exchange the claim tag somewhere, but basically you leave it at the T1 or T4 arrivals area and the coworker picks it up for a small fee (like $8 per day or so for smaller bags)

A lounge attendant could certainly store an envelope with a claim tag with your friend's name on it

p.s. as far as security - T2 has an elite/premium cabin line again (YAY!), and word on the street is that going through security atT4 is a breeze, again thanks to a premium customer line.