You sure can. Simply cook off the steaks, and while they’re cooking fill your cooler or a sealable container with very hot tap water and let it sit. Take care not to burn/scald yourself! When the steaks are done, wrap them tightly in tin foil, then in a towel. Empty the heating container of the hot water, put the wrapped steaks in, and seal the container. Residual heat will keep the flank steak warm but not dried out for an hour or more.