You can already do that.
You can punch in the the exact frequency by using the keys on the front panel - just the same way you would punch in numbers when entering the tc or date.
Or as an option - which I use - is if you push in the menu knob as you rotate you move in 10Hz increments vs 1Hz by just rotating. I will use my index finger to push on the menu knob and rotate the knob with my thumb and middle finger as I listen. When I get to the point where I want to be I will release my index finger and just rotate in one Hertz increments to fine-tune.