Choose Snapping Point? I have a building block that has a cube for the ceiling, walls, and floor. It also has a blast door that overlaps the walls to fit into the next building block.
The problem is that when I align the building blocks together, I want to align the edges of the walls together, using snapping.  When I try to do so, however, it snaps using the edge of the projecting blast door to the edge of the opposite wall, instead of wall-to-wall. I'm snapping from corner to corner. I made an example image:

It would be nice if I could still use snapping, like temporarily choose a specific vertex to use as a snap. What is the best way to do this?
This is the workflow I've found for doing this repetitively in Object mode.
The setup:

Pivot set to '3D Cursor'
Snap-magnet: 'Off'
Snap set to 'Vertex' and 'Center'. Because of the 'Pivot' setting, 'Center'  refers to the location of the 3D Cursor at the start of the move.
(The active tool is 'Tweak'.. it always is, for me)

The moves, for each snap:

Shift-Right  drag the cursor. Once you're in charge of the cursor, you can release the Shift.
Still Right-dragging, hold Ctrl to snap the cursor to the desired 'From' vertex. You have now established the snap 'From' point.
Now Left-drag the 'From' object to the 'To' object, with Ctrl, hovering over the target 'To' vertex. The 'From' point will snap to it.