Keyboard shortcut to “Comment” a line in NANO?

The simplest workaround I’ve found:

• Comment-out:
  set the cursor at the first row that should be commented-out
  hit twice ‘M-R’ (or ‘Alt-r’; in order to Replace a RegExp)
  Search for: ‘^’
  Replace with: ‘# ‘
  Replace this instance?: ‘y’
  press ‘y’ for each row to be commented-out

• Comment-in:
  The same procedure, replacing ‘# ‘ by ”