Even if you were only giving a radar service to one aircraft at a time, I doubt you'd be able to pay sufficient attention to the aerodrome outside the window at the same time. Even though there might not be any aircraft moving, you still have vehicles, wildlife, lighting systems (all of which have infringed / failed / generally tried to ruin a quiet shift for me!). Don't forget the radar monitoring to check for terrain and airspace compliance, any pop-up traffic to call etc etc on the inbound, and that's without even doing the vectoring.....
I do agree that it's desperately frustrating to be watching the inbound on the ATM without being able to expedite their arrival, but I reckon in this case the regulator is absolutely right to insist on a separation of the two tasks of APR and ADC. (Consider the attempts to reduce operational distractions both in ATC and on the flightdeck, and it seems impossible to then justify imposing a fairly significant task, removing attention from the primary ADC task, purely to a customer's economic benefit).
The answer is for the airlines to be making noise about this at management level, and insisting that they receive the service that they have paid for, and are entitled to.