Hold one side in an isometric contraction while the other arm moves through a dynamic (concentric and eccentric) movement. You then switch sides.
This simple modification not only helps you to create a new training stimulus, it also creates muscular overload by increasing the time under tension (TUT). By increasing TUT, you increase metabolic stress, a key mechanisms for growth.
A cadre of coaches discuss various bodybuilding and powerlifting topics, including the wisdom of trying to build size and strength at the same time, and the relative benefits of isolation movements vs. compound movements.