World Composition - how to use test maps?

For anyone that is using World Composition – how are “test maps” utilized without being automatically loaded via the WC system?

A few examples: simple “greybox” spaces to test prop lighting, or physics behavior, or animation.

For context - our game consists of a very large building with dozens of dense interior rooms. We plan to implement World Composition this week using a clean project, and then migrate our demo work into this new WC structure. We’re opting for WC for its organizational benefits, since our rooms are so dense, we anticipate ~250 sublevels need to be created.

Many thanks in advance!