Here's an idea that might not make me any friends.
Instead of having the Krayt dragon call scare off the Sandpeople why not just have Ben appear right next to one of them while they were trashing Luke's speeder (as if he has used his Jedi stealth to sneak up on them).
There could be an insert of a Tuscan looking up and see a robed figure right next to them and stare into his hood.
The line, "Hello there" could even be shunted slightly back so he addresses the sandperson and not Artoo.
His spooky nature and possibly his reputation could do the rest.
That way you don't have the somewhat odd shot of an old guy in a dressing gown making funny noises while approaching the more formidable looking alien chaps with spiky mummified face masks on.
He could then check on look and beckon Artoo out of hiding with the remainder of the lines.