To start I suggest combining several weighted ab exercises into an abs super set circuit. (EX: Rope cable crunch, plate seated twist, medicine side to side bounce)
Along with being a major time saver, ab circuits are cardiovascular, which over time will allow you to see those abs being built by the weighted ab exercises.
When your body becomes accustom to this new work load get creative and pick five exercises that will develop all the muscles in the abdominal wall and do 8 to 12 reps of each, one exercise after the other, until the circuit is complete. Then rest and do them all over again.
( Special thanks to guest models, Husband & wife Dan and Julie Frey )