We have a similar thing going at Aberdeen. Although it has been available for a few years now, we have recently made the procedure more formal by offering the clearance on start up if it has not already been requested. The driver behind this is the European Action Plan for the Prevention of Runway Incursions - a fascinating read and imprinted on my mind for years to come no doubt! An airport Managing Director's Directive has also been issued to bring this to the attention of operators.
We currently issue clearances without the squawk as that is usually obtained when the aircraft requests start, however I'm aiming to improve on this by late January when the squawk will also be available a short time (between 5 and 20 minutes) before start.