like the earlier poster said

when your feet reach horizontal positioning, pull up hard with the front in your strap/clip/w,e and then push backwards as hard as you can as well, do this from the saddle or leaning forward how ever you want to, maybe start the skid out of the saddle and then bring your weight back

the more weight you have over the rear wheel, the faster you are going to stop. so..... try and do this from a seated position if possible, pulling on the handlebars for some leverage is recommended

if your curious about how little force this is compared to a front brake, use your front brake and then try to do a little skid, makes it effortless and this is because all of your weight when you slow is on the front wheel anyways, its really really easy to lock the rear.