Default Rooting a locked HTC One with broken volume down key


I have a locked O2 (UK) HTC One and the volume down key is physically broken. The volume up key is fine and everything else seems in working order.

I have never rooted a handset before and thought this would be a good one to try. Imagine my amused surprise when I saw that the Volume Down key is not only a key part of resetting the lock screen, but also of the Rooting procedures I have briefly browsed!

Is there a way for me to do this or does the broken volume down key eliminate the possiblity? I don't care about backing up the handset etc. If there was a way to just wipe it and install stock Android or a custom ROM, that would be fine.

Any pointers gratefully attempted.

Thanks a lot.