If you disable autoRead and rememberReadPosition, STM will never Rebuild upon enable. I'd still like to go back and optimize the Rebuild() cycle itself (someday...), but I think manually preventing it from rebuilding should work for the time being - especially if the text your displaying isn't changing.
So... A check on a fleece jumper/drawstring to make sure the new string is different than the old one might be a string comparison check, but it's a lot lighter than rebuilding the whole thing!