http://www.kregtool.com/information_...g_pro_pack.pdf
Page 21 and 22 talk about aprons. They say to use a corner brace or a gusset to reinforce the corner. they do not show how to do the brace (maybe they do not recommend doing the brace with pocket holes) but they do show how to do the reinforcement with a gusset and pocket screws (maybe thats their recommended way).
George