A simple rotation of the sandbag (or kettlebell, if no sandbag is available) while descending into a reverse lunge will challenge your strength and core stability in the transverse plane.
When you add in the power of a swing, what you wind up with is a really cool explosive movement – the swing requires decelerating the implement at the bottom of the movement before you explode from the lead leg into hip and knee extension.
Maybe you're a bodybuilder through and through, but you still ought to know how to do some of the "old time" training methods like the split style. Besides, it may just put on some muscle, and that ain't bad.