I don't believe it is possible.
Remember when you are saving as a DWG you are saving actual lines, fills and objects - these are all in 2D so you don't have 3D storey levels any more.
Your trace reference if you could save it would be all jumbled in with your main storey (they share the same layers).
You will have to save a DWG for each storey and then overlay them in what ever other software you are using to create the effect of a trace reference there.
You can however print a trace reference either directly to a printer or as a PDF.
Barry.
One of the forum moderators.
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