Basically, the system would be related to a constant-speed prop i.e. N1 governor keeping the fan turning at constant speed. But the governor setting could be slaved to the throttle to simplify the cockpit.
Alternatively - Fan blade pitch (conversely "stagger angle") could be directly linked to the throttle, and then the fuel system demand slaved to fan speed to manipulate fuel flow. This would be analogous to "beta control" in a turboprop.
Or maybe R-R have a better idea...
