Welcome, @CarsvO!
A figure would help, but I think I understand your scenario: you want something like our flow over a heated plate tutorial, with a fluid-fluid volume coupling between the flow channel and a clone of itself. This will require some code changes in the OpenFOAM adapter, but it is doable.
Yes, uni-directional coupling is easy with preCICE (and easier than bi-directional).
The initial goal of preCICE was for surface coupling (as, for example, in fluid-structure interaction). But the design is generic enough that several people have now successfully done volume coupling with preCICE.
But beware that this is kind of unexplored territory and you will need to do a bit more coding than usual and we have no tutorial for this. However, this Pull Request to the precice/openfoam-adapter may help. If you want, you are very welcome to help drive the review process forward as well (this is a bit old and stalled by now).
We already have tutorial cases that are steady state, for example CHT with OpenFOAM and CalculiX or with OpenFOAM and code_aster. We simply assume that PIMPLE time is the same as a SIMPLE iteration.
There are a few more configuration steps involved, see the configuration page and potentially my thesis. For a more up-to-date and easy read, I also recommend the slides of our training session at the 15th OpenFOAM Workshop.
I am renaming the topic to give it a more specific title, feel free to follow-up with anything else we should clarify in terms of concepts already, or open new topics for any individual issues you get while trying this out. Of course, I would be very happy to know if you better understand everything now! 