Allow ghosting of unique structures in building mode

I'm planning out my island, and have the challenge of not being able to create a ghost of the captain's office. The trading post was the same way...wanted to make sure I could fit it in a spot that was developing, but couldn't put a ghost down to measure it against other structures.
You would (hopefully) just need to have a check to see if the item is already fully or partially built and it wouldn't get built just as if you didn't have resource requirements.
Another option: allow more than one to be built, but only one is functional, and we can tick a check box that indicates which one is functional. This could be a nice choice for aesthetics....(Someone might want to surround their island with a hundred statues of maintenance...but only one is providing the bonus). Technically, you're already doing this with the shipyard.
Thanks!