If there's one thing I've learned from Lucas, it is to make sure you have all similar objects in groups or stacks throughout the house. After sorting said objects, move the stack or group to another location where you can sort it again. It usually works best to move one item at a time to the new location, even if the item is as small as a magnet. Some good places to put things are on Mom's back if she's laying on the floor, on various couch cushions, or behind the TV.
Here's a video of Lucas sorting some larger items: