Originally Posted by FBinNY

If I read the OP's later comments correctly, his idea is very different from front freewheel. It seems he want's the ability to engage/disengage/ a fixed gear arrangement at will.

A basic overrunning clutch such as Shimano's old front freewheel system won't do the trick, and as others point out has no advantage over a rear freewheel.

But it's an interesting idea for fixed gear riders.

I have a vintage Sturmey Archer 2-speed fixed hub that I've arranged to do exactly what the OP desires. Using a 3-speed control, I have it set up with normal and low using the 1st & 3rd gear positions and have a dead spot or neutral in 2nd. It's nice for long descents, and I've used the feature in emergencies where cars have squeezed me to the curb and I couldn't have the right pedal come around to 6 o'clock.

To the OP, from a technical standpoint you're approaching this the hard way. You'd be better off putting your clutch into the rear hub, where for example you could route the control cable without dealing with clearing the rotating cranks.

Except fair warning. There's a rumor SA Taiwan is bringing back the TF hub, or maybe a 3s fixed, which would probably eliminate the need for your device. (maybe it's happened already, I don't follow all new items)