Why not just buy a ticket on a flight that leaves T5? USA 3000 has low-cost flights that depart from T5 (even to domestic destinations like RSW).
AFAIK USA 3000 domestic passengers are co-mingled with the international passengers in the T5 departures area. You can even arrive into T5 on a domestic flight on USA 3000.
So I assume you could book a one-way domestic USA 3000 ticket, ORD-RSW, check-in, clear security, have a look around, and simply leave. It would cost you about $70 but your curiosity would be satiated.