Create an action - 'Open in Notepad'

Start => Run => 'regedit'

HKEY_CLASSES_ROOT => *

Create a new key 'Shell' and then 'Open'

Modify the 'Open' value to 'Open in Notepad'

Create a new key 'Command'

Modify the 'Command' value to 'notepad.exe %1'

The result (when you highlight a file and right click):