What I try to put forward:
The only way I could think of to indent any line in the field UNSYNCEDLYRICS is to add leading spaces.
The number of spaces would be calculated by (<length of line> - <length of lyrics string>) divided by 2.
The result would be fixed and not dynamic.
You did not specify the <length of line>.
And you will probably not be able to do so as this value depends on the width of the text box for UNSYNCEDLYRICS.
You can modify the action that adds "MUSIC from Joe" to a string that shows "_____MUSIC from Joe`" (where the _ is a space character)