Preformed ribs are held closely to the swelling element and then are allowed to assume an expanded position to capture the ends of the swelling element. Many variations are possible one of which is retaining the ribs in a run in position with a band that releases by interaction with well fluid. In another embodiment the ribs are of a shape memory material and go to the enlarged state after a time and exposure to well fluids. The swelling action of the element could urge the ribs to the expanded position. Alternatively, a retractable sleeve can be actuated after a delay using a piston and a sealed compartment where a material must dissolve or otherwise go away before the piston can stroke to remove a retainer from ribs that can then move out.