Plumbing for toilet valve...

I needed to change out the tank components. I could not shut off the water since the valve seal was shot. I picked up a new valve and tried to use the old compressing ring hoping it would seal. Well over time it must drip. I would like to cut off the pipe behind the compression ring to install a new one but that will leave me with such a small stub I may not be able to get the coupler nut on to attach the new valve. So whats the easy way to repair this?
I was thinking of soldering on a coupling to extend it then attach the new valve.
I am not up on all the plumbing terms so please realize that. Any advice would be great.

I did think of that after the fact. Still if I cut the pipe it will be awfully short, even to solder on a valve.