Vans

converting is pretty easy if a little time consuming.
you will need a sheet of hard plastic, a drill, a saw, a marker pen, and a sharpe knife.
pull the insole out of your shoe.
draw round it on the hard plastic and cut it out using the saw.
place in the bottom of the shoe.
figure out where you want the cleat to be and drill though the shoe base and plastic.
cut round the holes to make the cleat sit a bit futher into the shoe.

most cleats come with a plate that can then be put inside the shoe and used to bolt the cleat on with a backplate.

not the best though as the base of the show flexe's under the cleat without the solid base but then there not designed to race with.

Make sure it's not a brittle plastic though. I'm not up on what plastics do what but not something like acrylic.