Here's how you can convert your existing layout to do this:
1) Click the Edit Layout button in the top toolbar and select Edit Document Viewer.
2) Click the document viewer's Options button.
3) Click Expand to Full Screen, turn on Cover Top Toolbar and turn off Show Initially.
4) Click the Edit Layout button in the top toolbar and select Edit Buttons and Fields.
5) Click the empty area of your layout (where the small document viewer was) and add a different field there: Notes Viewer, or a multi-line custom field. Then resize and drag it into position.
6) Click the Edit Layout button in the top toolbar and select Save.
Then you will just need a way to switch between your notes and your lyrics. One way is to click Edit Layout, select Edit Details and set Show/Hide Document Viewer to Two-Fingered Tap.