Ok, I deal with separation anxiety... in dogs.
I fully appreciate your son is not a dog, however on a cognitive level, small children and dogs have some similarities (and it is these similarities that allowed dogs to associate themselves with humans successfully)...
In NO way would this be acceptable in modifying behaviour with any other species.
If I were to suggest a protocol like this I would be thrown out of my professional body.
What they are attempting to do is to teach him that seeking attention does not work, give up, that asking for help does not work, that he is in fact completely powerless, submit to it and give up trying.
IF it works, what it will achieve is a child who stops trying to get help for himself - it won't make him HAPPY about the situation, it will simply suppress the behaviours he exhibits, for a short while. You will almost certainly see what dog trainers call 'fall out', ie, other problems cropping up elsewhere.
Take him out, don't go back.
Build his confidence and security and independence at HIS pace, give him choices (or the suitable and appropriate illusion of choices), play games where he goes away from you and learns that this is safe to do (start with a few feet, build up to out of sight round the back of the sofa or out the door to the room)...
But this.. whats going on now, is not necessary, its not beneficial, and its horrific and I feel SO angry at the people who have made you think this is necessary or ok, and have made you feel like you are the one with a problem in feeling uncomfortable with this.