I think Beckham should still go with the England squad, but as a 'morale booster'. He could be the new Ken Bailey, dress him a union flag suit and top hat. Before the game he could go around the dressing room raising morale and offer Keeganesque remarks to the younger players like 'take deep breathes'.
During the game he could wander round the pitch side picking up scarves, sign autographs and stir up the England supporters.