Just buy the cheapest one way ticket anywhere with the airline that will get you to the gate area you need to go to.
Had a similar situation a few months ago at LAX...needed to be in the Delta terminal...at LAX T-5, T-6 and T-7 are all accessible once you clear security...just bought a cheap ticket on United and took the tunnel to T-5. Cancelled the ticket within 30 minutes. Just to be sure, I cancelled the UA ticket online and I called UA as well.
Another problem is that there are conflicting rules about gate passes depending on which airport you need one. At LAX, all of the agents recently have told me that they don't exist at LAX.
At DFW it was problem at all. I even took a pic of the DFW gate pass and showed it to the DL employees at LAX and it didn't matter a bit. Was still told it can't be done at LAX.