90% of the time the cause of this problem is because the spring inside the gas door is missing. The spring is simply a little clip that pushes the door outward once the lock is released, think of the spring as a door hinge.
1. You can get someone to push the door while the 2nd person pushes the release button.
2. Slide a piece of index card or thick piece of paper into the gas door before pushing the button. This is what I am doing right now for the last 2 years.
This happened once on my ES, I would have someone push the button and I would open the door using a piece of blue 3M tape (doesn't leave sticky stuff or harm paint).
The funniest time, was when I was alone in the summer at about 2AM and there was no one else around, I mean no one. I guess the store attendant was in the bathroom or something. I used a q-tip and a length of dental floss. Smushed the end of the q-tip in the crack so that the cotten head would bunch up behind the edge of the fill door. It was soft so I didn't worry about the paint. I then tied a lenght of dental floss to the other end of the q-tip and held that taught in my right hand. I then reached with my left and hit the opener button while I gently tugged the floss to get the door to open past the locking mechanism. You get real creatvie when you need to.