Mario suggests using a mechanically latched connector.
It's just a part change... will consider during beta testing.

Possible latching ribbon connector:
609-3070-ND

Possible latching PCB housings:
https://www.digikey.com/en/products/detail/cnc-tech/3010-20-001-12-00/3441617
https://www.digikey.com/en/products/detail/amphenol-icc-fci/71918-120LF/1002070
609-6190-ND

Another possibility is to add holes at connector top/bottom, and then zip tie them in place.

...

Since ribbon headers mostly have the same footprint, there's no need to solve this before ordering the RevC PCB.  I'm going to order a few different connectors and see what works.

18S:
Seated connector height important, so it makes sense to get a low profile latching ribbon connector (because latching board connectors are quite a bit taller):
609-3070-ND

Could also use a latching right angle board connector:
609-86130202113345E1LF-ND (ordered a bunch)


...

12S:
Ideally we'd do the same as 18S, but can't find any latching ribbon connectors in stock (e.g. 609-3563-ND).
Latching board connectors:	
HRL14H-ND (ordered a bunch, but EOL)
609-5970-ND
2057-MHR-14-HUAL-ND

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Solution:

Ordered right angle latching connectors.  Solves two problems (the other being the lack of vertical height).

12S: HRL14H-ND​
18S: ​609-86130202113345E1LF-ND​

Need to move J13 down so it doesn't xfere with fan mounting bolt