How can I wind back the rear brake cylinder (Opel Zafira with ABS)?

I am trying to change the rear brakepads on my Opel Zafira: the problem is that after removing the old pads, I can't wind back the cylinder. I have tried to push the cylinder in by using a carpenter vice (L-shaped), placing the 2 pressing points one on the back of the cylinder (where the handbrake lever is) and the other one right on the cylinder, but in spite of my applying very strong pressure, the cylinder won't move! I don't even have enough space for replacing my old brakeshoes (worn out and thin ones!). Can anyone help? (Or I'll have to have the car towed to a mechanic's). Thanks