You could try to pull the vein out from the head end (using tweezers :rolleyes: ), but the vein might snap. Otherwise, I doubt it's possible to keep the shell 100 percent intact. The least invasive thing to do is simply split the shell on the side with the vein -- no need to actually remove the shell -- and pull out the vein. I assume you're using headless shrimp?
But you know, it isn't always necessary to devein. Only is the contents of the vein are gritty, or for aesthetic reasons if the vein is very dark.
"Notorious stickler" -- The New York Times, January 4, 2004