However it needs to be done. I imagine I would build a piece manually in the Editor, then convert it into BP actor (unless that’s not possible in UE4 currently). I am sure I could build it as BP actor to begin with. It’s just not designed to be worked with like that IMO.
The custom set piece will be on the grid, as if it was generated by DA (2 x 4 let’s say) with connecting junctions also placed on the grid (so a door or a hallway entrance, for example, would be located where they would have been if DA would generate it; not offset or anything like that). However inside of that 2 x 4 set piece nothing would be on the grid. I should probably make a sketch explaining it.