I've used this trick for overweight hand luggage many times without incident. When I go up to the luggage counter I wheel the cart with my luggage up and as I unload it all I stow my overweight carry on behind the counter where the agent cant see it and when they ask to weigh my hand luggage I weigh my little knapsack I am carrying. When my luggage is finished being weighed I unobtrusively wheel my hand luggage from behind the counter along with me. By then the agent is always looking at the next person in line and not paying attention to me