I think what I am going to do (please shout if anybody has a better idea!) is to buy a "standard" garage door closer with a wired wall switch included. Then, surely you can just replace this wall switch with a Z-wave version? Add a Z-wave door/window sensor as well, and there you go.
One problem that I foresee is finding a garage door closer with a wired switch - most seem to boast wireless wall switches (in addition to the key ring remotes you usually get).
I think I would also need to add some sort of break-beam sensor as well, just in case I'm working on the car half in/half out of the garage. Does anybody have any recommendations for this?
EDIT: This looks just the job if my idea is going to work... http://www.doortronic.co.uk/acatalog/Lift_King_LK800_Professional.html#