I don't understand what you're proposing. If it's a group owned aircraft, i.e. shared, I can't see how you can fly it on your own without being part of the group.
Or do you mean that you and your friend will fly together, he or she will sign the tech log and be flying the aircraft as a group member though in reality you will handle the controls and log it as PIC?
If the latter, you are on very dodgy ground from both insurance and legal points of view when/if you have a mishap. Sorting out who was really PIC will be fun (not).