It's not what you should be doing and that SLP didn't understand stuttering. But most don't. You're right though that our stuttering usually sounds worse to us than others and all the extra things we do to try and avoid it thinking it sounds better, is actually more annoying and exhausting to the listener. I'd call it a trick more than a technique, but in the end they're the same things. Finding a good therapist who gets it is the hard part. I would try to reduce use of baby voice in the easiest/safest places where you find yourself using it. You won't be able to stop it in harder situations.