but you can save brick ownership, so they're forking over the information anyway, what you could do is just save the whole thing, then go through and delete the bricks not on your baseplates?
Brick ownership is only for bricks touching the ground directly. Any bricks that are attached to other bricks gain ownership from the bricks they are attached to, in other words, the bricks touching the ground.
If you really wanna figure out how you can save only your own bricks from just the baseplate, positions, rotations, and UI names (not datablock), go ahead.