Blue Print add-on to existing base

I was building my base and got to thinking, it would be easier to be able to have a "add-on" blue print where you can place pre-fabs onto existing bases. Like if I wanted to build a gun tower, I can just build a blue print and place it onto my base.
I've also made "fake tanks" using concrete and would love to just place them all over my base without having to rebuild it block by block.