In NX 5 you can use the new Instance Geometry function to associatively copy (instance) all or part of a sketch resulting in essence the same thing as creating an instance inside the sketch. Granted, it's an extra feature, but the results should be usable for what you're attempting to do.
John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA
Thanks for the tip John, that's what I'll end up doing I think.
It'd be much nicer for future manageablity & neatness to be able to do it within the sketch in this case, but your suggestion is definitely preferable to instancing the feature after.