You can extract the Geometry from the Family Instance as shown here:
Might be possible to use some geometry converstion from the “Sheet Width” / “Sheet Height” parameters (from metric to imperial, as I think this is what sheet-space uses)… might try a little test after lunch… or now.
Took some video of the dynamo user group. Not the best but its something. Think there gonna film the next. Never used youtube to upload so hope that link works