I'm lucky I guess, I live close by, I often go home for lunch..
But consider this possibility, along the lines of much of what Bernhard has said elsewhere in these forums (I'm surprised he didn't mention this in his above post!) - Use your lunch hour to do "away from the piano" practice.. I just did this at work yesterday actually during a break, I loaded up a PDF of the score to a Beethoven Sonata I am preparing to learn, and I listened to the recording while reading the score.. I did that a couple times, and then spent 15 minutes working on a bit of harmonic analysis of the piece.
You don't need a piano to practice.
-Paul