You do what Sorch did and what Kat is suggesting and you'll be sayin' "good bye" to P.F. in no time...
BTW, in case you didn't understand the exercise just think back when you were doing backflips off the diving board... That is the position... It will stretch the crud outta the plantar and will really help...
The Crooks will help, too and a lot cheaper and better than the Berks...