Tried it both ways (same sketch and different sketch). Still no avail...guess the simple delete and redimension will have to work for now.
If you want just make a block with a simple cut-extrude feature, goto new drawing and dimension the extrude. save both, the drawing and the part. close the drawing. Delete the cut-extrude and sketch, save and close the part. Open the drawing and your dimensions will be dangling. See if you can reattach them to any of the edges.
Our VAR was able to do it last night in 2005 so we figured it was a 2005 option. I tested it on our machine here that has 2005 and no luck. So I am assuming that it is an option somewhere but I can't find it. During the brief class that we had last night, our VAR was mentioning that you click on a red box to reattach references and dimensions but I don't see any red boxes.