You could always catch the bus to Hatton Cross and walk down to the Concorde hangers, takes about 10 mins to walk from Hatton Cross station. You should have time to do that with 5 hours to spare. There is usually at least one Concorde outside to see (maybe GDB could arrange one to be out the back near the A30 for you so you don't have to walk as far
The bus is free to Hatton Cross too - take the 285 from the central bus station or T3
bus park. From Hatton Cross, walk over the footbridge and facing the BA
hangers (with the Traffic lights behind you), walk around the corner and take the first road on the right. Follow this road for about 1/4-1/2 mile and you will see a hanger on the left, behind a huge car park. This is where Concorde lives. If there are none there and the hanger doors are closed, keep walking to the big gray BA
World Cargo Building on the corner by the little roundabout and follow the fence all the way down past the side of the hanger, there is usually a Concorde parked round there too.
Hope you get to see at least one. Seeing it on the ground is better than not seeing it at all.
"She Rolls, 45 knots, 90, 135, nose comes up to 20 degrees, she's airborne - She flies, Concorde Flies"