This little plastic coupler will let you connect two HFBR optical cables together.
It will work with either latching or non-latching connectors, as shown here:
If you're using the latching ones, note that the top surface has small indentations for the latch to grab: the bottom surface does not have those.
This is an experimental device so please test it carefully for yourself.
You can download the stl file for this here to print yourself: hfb_coupler 1
We print them on a Prusa printer using PETG with a 0.22mm layer height.