You have set quite a challenge to do this w/o moving your hands away from the home row, but we'll see what we can do! ;-) I think you have several options!
You have alluded to inserting a comment, and a quick way to do that is "Ctrl-A # Ret". How easy that is depends on where # is on your keyboard. A quicker way is to use readline to bind a key to "insert-comment" (see here
) By default this is Alt-# which is quite easy on my keyboard. If you don't like it you can change it too.
Yet another method would be to run gnu screen all the time. http://www.gnu.org/software/screen/
Then you could "alt-a c" to make a new terminal run what you want and alt-a alt-a back (and then alt-a alt-a between the two as much as you like...) I do this when I ssh into a box.
Finally if you are running on a vt of course you have the options of alt-1 alt-2 etc to get to different terminals.
If none of those are satisfactory then you are very hard to satisfy! :-D
Edit: ok you have already said you might not have screen installed... so you don't like that one, so here is another option to replace it...
Readline also has a "backwards-kill-line" which by default is bound to "c-x rubout" (for me that is ctrl-x backspace). Then do what you want and on the next line yank with ctrl-y to yank back what you deleted before. Again if you don't like the bindings you can change them.