When you put him down, put one hand on the scruff of his neck and put only his rear feet on the ground.

That gesture should immediately send the puppy into a relaxed state. Back feet on the ground, front feet up in the air, you are holding him up by the back of his neck. As the other dog(s) gathers around, bringing him to the ground. His tail might be partially between his legs, if so pick up his front feet, until he relaxes. Let the other dogs sniff him, they should accept him, if he is relaxed.