First, line spacing
is paragraph-level formatting.
Try
exactly the size of your expanded character, in points.
Otherwise, you could use
WordArt for your first letter.
Word will mark the remainder as a spelling error unless it forms a complete word without that letter.
WordArt is also on the Insert tab. Note, WordArt is no longer part of your text. It is a graphic.
This is not the case with the other methods.