If your recessed cans are rated "I/C" then you can have insulation packed against the housing, however, if they are not, I know of no way to safely insulate them and still allow adequate air circulation to cool them. They have thermal cutoffs that will trip if they get too hot. If ice damming is your main concern, make sure you have adequate ventilation in your attic to exhaust any heat buildup in winter. Make sure vents are not obstructed, as the attic is designed to be as cold as the outside air. If energy conservation is also a concern, consider either changing to I/C rated fixtures or replace the recessed lights with flush mounted ceiling fixtures and patch the holes. Good Luck.