What type of molding are you looking to make? You could try using walls or beams to make the curved part in plan. Then convert to Morphs and rotate up into position.
GDL also offers a means to do this. That is what I ultimately used in response to a similar question I had a while ago (AC 11 or so): Plaster pattern on a barrel vaulted ceiling
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
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