Make sure he's well fed, make sure he's not in shed or otherwise stressed and then just pick a quiet evening and get him out. No muss, no fuss, no letting a bunch of people mess with him - just you and the boa sitting quietly. Put on some tv and just relax with him for a bit. Just let him get used to you again without a lot of anything going on. A couple of nice handling sessions a week and you'll be back on track with him in no time.