Bleeding Giant Root brakes.

Hi, tried to be clever last night and bleed the rear brake on my Giant Escape R1 (MPH Root again) but through a combination of trying to use a nasty little adjustable wrench and being a bit of a spanner myself I've managed to round off the nut on the bleed nipple...

Current plan is to use a set of mole grips to undo the nut but obviously this will render it well and truly knacked so it really needs replacing. Does anyone know whether it's available as a spare part (either from Giant or as a generic component)? I'd rather leave it on and have a weak rear brake than take it off and not be able to replace it. I've tried searching online (including the two sites mentioned above) but haven't been able to turn anything up, although I can't access ebay at work.

I did purchase a Giant bleed kit which included 'olives and pins' but there was no explanation as to what these were for and I've misplaced the bike's manual. These include what look like replacement nuts but are hollow with no nipple. I'd be really grateful for any light anyone can shed!

Cheers

Liam