I completely agree with Keygrip's comments. If one is flying and the other doing R/T then that isn't really CRM as there is no specific flight oriented goal ascribed to those divisions of tasks and activities.
Without want to teach grandma to suck eggs (what the hell does that mean anyway?) CRM is the acceptance of fallibility and personal limitations, it is a process of situational awareness maintenance, risk mitigation and resource awareness which is just as relevant to single crew situations. In many ways single-crew CRM encapsulates many attributes of basic airmanship, but without the wishy washy platitudes.
Multi-crew ops are effectively an extension to the core fundamentals of single-pilot CRM - additional procedures to help ensure that the flight deck crew have the same situational awareness picture. The allocation of duties and tasks is a means to that end not the end in itself.
The reason in an airliner that the PM (pilot monitoring) handles the R/T, moves the gear, updates the FMC, etc, etc is not just to permit the PF from concentrating on the critical task of monitoring the flight path, but to also keep the PM in the loop. One example is in the cruise, enter icing conditions, it is the PF's responsibility to request anti-ice, the PM's responsibility to switch on anti-ice. This is a trivial activity and would have been much quicker and easier if the PF just flicked the switches himself. But it is more important that both know the state of the aircraft.
So if sharing a flight and wanting to split the tasks I recommend discussing how splitting those tasks will keep both guys in the loop and the sense situational awareness and aircraft state is the same between the 'crew'.
I'm struggling to find references but this is a fairly well established phenomenon, called "risk shift" I think. A small group accepts a greater level of risk as a "team" than any of the individuals would on their own.
It is part of the JAA ATPL theory. Modern SOPs deal with issue quite well. For example we have criteria that define a stable approach. If we aren't stable then we go-around, no debate. I think the psychology in a modern well run airline is fundamentally sound in this regard. One example from my recent experience was as we approach the top of descent I got weather for the destination, the wind was on just over our tailwind limit and the SCT ceiling was on our circling minima. We decided not to try an approach and to divert prior to the descent. I actually wondered if we had been over cautious, perhaps we should have had a go, a thought that now treat with incredulity.