Yes you can. Create an assembly, add another part (which can probably be empty, aside from a coordinate system), then add your sheet metal part. Merge the two, using the other part as the active part. The other part will then be a solid with the features of the sheet metal. I have done this, but with features in the other part. CREO then merges the two. I use this to create complex channels that are on the inside of a cylinder.