I've used the tape trick for corns that have escaped but those were much smaller. I would also recommend something like painters tape that's meant to come back off so it doesn't hurt him. Run it along the walls, behind furniture, and across any opening he might use to get out such as doorways. If he's going into blue though, he may not move much at all so pull everything away from the walls, check inside furniture such as couches, desks, etc. and work your way across the room. With the tape, also be sure to check it first thing in the morning. If you do catch him on it, use a little oil to help it release from his skin. Hope that you find him soon but don't lose hope. I had a corn girl (adult) missing for close to 3 months when a friend was borrowing her. She was found upstairs, hiding under the vacuum cleaner, digesting a meal she'd caught. Snakes can be amazing survivalists so don't give up on him.