Linear dimensioning along an arc?

I have a rolled tube that requires tabs welded on at certainlocations along the radius of the tube. The raduis is to large tous angles from the center, so I would like to use a linear ordinatedimension from one end of the tube to the other on the outer face.If any one has done something similar to this, could you give mesome pointers on how to make this work.

Thanks

R.S.SolidworksDrawings And Detailing