Something like this might be more effective than plugging the lines:
http://www.amazon.com/Dorman-13911-Master-Cylinder-Bleeder/dp/B001SG8ZC0/ref=sr_1_1?ie=UTF8&qid=1406230009&sr=8-1&keywords=bench+bleed+kitIt's basically a bench-bleed kit, but "bench-bleed" is just a term for bleeding a new MC. You can bleed it while it's installed using this kit. As dakdave said, unhook both lines and install plugs - or in this case fittings to which you attach rubber lines. Route the rubber lines back into the fluid in the MC. Pump the pedal a few times and it will blow bubbles into the fluid until all of the air is dispelled. Replace the cap!! The seal of the cap will prevent the MC from draining itself again. Reinstall the lines and bleed normally (again, I would gravity bleed.
The pedal should be back where it was.
Just an aside, your "mechanic" should know this....just sayin'.
