If you absolutely have to do this for a limited number of people, create for each a phantom extension for each, build a sys fwd path to that phantom, and set the sys fwd path to kick in for CO Recall call type (be sure it's above other fwd pats, list hunts top down). Then give user a Secondary Call Key representing that phantom. Now recalls will appear on that key and user will need to press the key to answer, assuring he knows it's a recall. Convoluted and time consuming if you need to do it for a lot of folks.