Personally I would recommend against eating 5lbs of meat in 1 hour, think about it, that's = to a bag of sugar in weight. Does nothing good for your insides (neither the weight or the ground beef. You can actaully cause damage to your body.
With that said...
You really should have been eating massive ammounts of food for days prior to the event to stretch your stomach out a bit. As previously stated, fasting for 24 hours actually shrinks your stomach.
Hope you made it out alright. Citric Nitrate is your friend. But unlike the burger, don't drink as much as you can in a short time - can be dangerous, especially with 5lbs of meat in your gut!