If it's a standard bear claw latch used by most of the shops it looks like this with the panel off.

latch.jpg

The rounded piece of flat stock with the hole that you see is pulled up to unlatch the door, and there's a second piece running vertical that's hidden ("L" shaped, pivots at the corner). I'd think that you should be able to reach in through the "U" opening on the panel with a thin screw driver and lever it up without too much hassle.