Pardon my lack of flying knowledge about IAH and its sterile Global Entry Enrollment Center, but I'm really struggling to find the info on this that is clear to the novice.

My simple question is this (because my city's enrollment interview period is 3.5+ months out until availability), it's inexpensive to fly to IAH, so can I fly into Terminal A on Spirit in the morning, ride the Terminalink/Skyway (post-security intra terminal people mover) to Terminal D/E stop, get off and walk up to "sterile" CBP office for interview (evidently by Ruby's, which I also can't seem to find any map of), or do I need to have an international ticket to/from Terminal E in order to get into there? I know I'm beyond security on Skyway, but I still wouldn't have a boarding pass for Terminal E and not sure if the office is before or after boarding pass review when coming off the Skyway (I can find no map that showscenter clearly for someone who has never been in there). Currently those are the only soon interview times for a plane flight that costs $70 rt. If I try to fit it into the public enrollment center on another floor, flight times do not line up, and the flight cost goes to over $200. Please help me know if IAH sterile CBP is a business option when flying into IAH domestically just for that.

THANKS!!