You are asking for a foreshortened radius dimension. I did a quick check in the PTC knowledge base and noticed it is a "what's new" item for Mildfire 5. We use 4 here, so if you have 5 you may be in luck.Otherwise the alternate technique is given in TAN 114578. I noticed foreshortened radii were asked for back in Pro/E 2001 and they finally have it available in MF5. I know foreshortened radii were available in Solidworks 2008.