I THINK the way to do this with the Mustang configuration is to put a block on the accellerator pedal, heel on the brake, flick the throttle with your toe.
You need to play with the thickness of the block but the "universal" stamped steel clamp on works pretty well.
I used it when I autocrossed but found it to be difficult to live with otherwise so it's now long gone.
It raises the pedal about an inch. Racers have been using blocks of wood for years but anything that can potentially fail in use and block the pedals, like this, is not necessarily a good idea and caution should prevail.
Consider that many racers of the day were like jockeys. They were slight of body and had little size 9 feet. Even so you need to match your driving shoes with the car and the pedals.
Miles is often shown wearing his black Thom Mcan street shoes. You don't start to see dedicated racing shoes until a little later.
I have to use a Ne Balance road racing sneaker because the soles are molded to curve in with no square edges to catch on anything.
You have to do what works for you. Everyone is different.