HI Ben,
I am surprised that an alternative way to do this has not been mentioned. Adding invisible spacers objects always bothered me, personally. Have you looked at NonMusicalPaperColumn.line-break-system-details settings? Please refer to the NR Section 4.4.2 Explicit staff and system positioning (for 2.19).
You can precisely adjust x and y coordinates of a system and have it only affect just the one system.
Andrew