I cant answer your question, Im not even sure if its possible, But Why would you want to upstream?
I want to be able to upstream wax on some jobs. And degreaser on heavy equipment.
Upstreaming soap under pressure does increase the speed you can wash, in my experience. The disadvantages are that you will bypass back to the pump or the soap will go to the tank. You will also need to learn to meter your soap. The dilution ratios are actually less, in my experience for the same cleaning efficiency.
A lot of people claim it will damage your pump, or your packing. That has not been my experience.