First off, Shoppers has GREAT ear plugs. Get the orange ones, which are rated for 33 decibels. You can buy them in boxes of 6 pairs.
I have never really found a way to stop myself from blurting, but what I have been able to do is channel it into a more socially acceptable format. I'm lucky that mine comes out in the form of music, because pretty-much everyone has had a song stuck in their head at one time or another, and so I just explain it that way...have a song stuck and it won't go away, so I'm singing it under my breath.
I have been trying to teach Little easy child how to whisper his, so that they're not disruptive and they don't cause him to get in trouble at school. He's getting better at saying them quietly, but it's hard work.
With difficult child, the only thing that seemed to work was to give him a music player and headphones. Of course, then we had to deal with the off-key singing, but that was much more bearable than the high-pitched squealing and other blurts.
To give you a sense of what it's like, it's a bit like having an itch. If it's totally inappropriate to scratch that itch, then you can usually control yourself from doing so but it's hard work. Trying to stop blurting is a bit like suppressing an itch. Hard work. I can usually maintain when I'm out in public a bit better than at home (so poor husband has to deal with my twittering because once I'm at home I have the freedom to let it out)
I don't know if any of this is helpful, but perhaps trying to explain to your son that there's nothing wrong with the repetitive speech, but there's a time and a place for it. Maybe if he can suppress when it's really important, then he can be free to blurt when he's alone in his room, or something.
Just some random thoughts.
(On a completely different note, I love your screen name. I remember when PET uttered the infamous "Fuddle Duddle" too)
