This might not be what you are looking for but you can set CSS of the TextBox so that it is entirely invisible.
I think it's "color" "background" and "border" all set to "transparent".
You could then just set the text on changes made.
The textBox will still do all the work but you won't see it.
The trouble with any of these methods is getting a text position marker. That I don't know, apart from the entirely terrible method of having special characters which are added and subtracted from the string.