You could use the Fuel Transfer Main 1 & 4 switch to move the C of G forward.
Creative fuel pump selections with all the X feeds open using the jettison system would get the C of G aft quickly but only to a point system logic would cause reserves to tranfer as normal moving the c of g forward or stabilizing it, you could stop the jettison and continue to "burn" the c of g aft again with x feeds all open and creative fuel pump selections.