Muzz has one on his SP1.. he rigged a hose to the rear master and has both foot and hand (left) operation.... he only drags the rear with the hand lever so it is quite effective..

I just use the rear brake pedal...I was somewhat fortunate to have ground down my stock brake lever in a minor wet weather spill which meant that the quirky foot position Chubb's referring to is pretty comfortable with the narrower pedal (foot rolls to outside of pedal and doesnt take any major readjustment).

I tend to use it mid turn and sometimes coming out of tight turns like T8 at wacky or T2 at EC to minimise the risk of spin up/ high side..Allows a little more throttle which in turn will also keep the front down ....

but as per Chubb...Im not really fast enough to need it, just try to practice it to get it down pat..