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Sorry, I don't really have a solution for you. That is just unavoidable with LAN parties.
But, if you are like me you have cables out the ying-yang so you could take all the required cables duplicates and keep them in a bag(Power, CAT6, DVI). You get could a wireless keyboard & mouse.
That would make it really easy. When you are ready to go throw your wireless K&M in the cable bag, unhook your monitor and tower, throw it in the car and go. Oh....and don't forget the headphones.