Axis labels for sheet metal

I have made two drawings, flat and bent, according to this advice (http://communities.ptc.com/message/14602#14602)

but now I need to reference the center of an arc on the flat drawing. Yet when I go to add an axis in the model, I canonly add an axis to the model prior to the flat pattern command.

How can I dimension to an arc on my flat pattern drawing?

Thanks