Manipulating at lines of StringBuilder

>1) I have a variable...Dim sb as StringBuilder.
>2) I assign a bunch of lines to sb.
>3) I can get all the text back as a string with sb.ToString.
>
>My question is how can I programatically update the various lines in
>sb? For example, let's say that I want to add 2 spaces to the
>beginning of every line in sb. Is there a way to do this easily? I
>don't see a way to even read the individual lines in sb, never mind
>add text to beginning of each.