Er, why don't you want that? The usual model is as follows (note to others: this is not my area of expertise, please correct me if this is inaccurate):

You bind a port as a listening port. When connections come in, you accept them which creates a new socket on a random port to handle communication with the computer that just connected. You then (if more connections are desired) set the original listener socket back into listen mode to accept another connection.

It shouldn't matter which port number you are using to handle communications once a connection has been established.