Frozen Metal Valve Stem

[TheNeek]

I'm trying to polish some outer lips. I've run across some metal vavle stems that I can't remove. They are old school. Flat head screw driver slot in the back, big 14mm nut on the top. The nut holding the valve stem to the rim half is frozen to the valve stem. It requires more force than I can hold with the flat head screw driver. It's starting to slip out of the slot. I've tried penetrating oil, pliers. I'm getting close to just trying to drill out the stupid thing. Any advice or special tool? They are very similar to the ones below. Only not so freakin tall.

http://www.brattons.com/uploads/images_products_large/02240.jpg