Never done it my proper boards,but I have on my softy and it was a massive fail. It was almost like surfing finless without the spinning fun of a Fin less softy
I use the old plastic Slater fins in mine as a thruster and it seems to be the best set up.
If you try and put bigger fins in a softy they will sadly rip your plugs out
In saying all that ,you have to be realistic as you are on a big floating wave stealing machine and control is not a strong point in a softy ,so no matter what find you use you will always be nursing turns
Rip the fins out and go spinning crazy mate(also will teach you super quick how to engage a rail)