I believe the answer is simply NO! This is based on a single experience where I had to check in at PTY for a Copa flight connection, having arrived from SJO on a Copa flight but with a different ticket (long story described elsewhere in FT). There was no transfer desk for Copa, thus I doubt that there would be one for Iberia. Mind you, going through immigration, customs, CI, and security took me an additional 20 minutes, thus not such a big problem (I was in C).
At any rate, assuming that you have not checked luggage, OLCI for your next flight is the only way to avoid the "long" connection procedure through the basement.
PS No idea whether Iberia can check you in at the gate...