shinya aoki uses a vicegrip to finish it.. theres nothing wrong with using a guillotine grip though.
i think the only important thing to consider is to make sure your using the bony part of your forearm, right under your wrist, to apply pressure against the side of their neck.
what may also help is, with the thigh pushing their neck, push off at a 45 degree angle towards their legs, rather then pushing straight across. i'm only assuming so because this rule applies with another similar choke that i use.
personally, i think there's tons of better options then a peruvian. especially when you consider the jap necktie... i dont think its very high percentage when it comes down to it.
if i've got a vicegrip and i cant knock the guy off their base in turtle, i use a similar choke that shinya aoki showed me in his dvd.
instead of throwing my legs over and whatever, i get the knee on his head side, and essentially put it inside of my vicegrip, so that its pointed on a 45 degree angle where his neck meets his shoulder.
i position my entire body behind my knee in a track stance with both feet pushing off the floor, and pull the vicegrip on the far side of his neck while i shove my knee through the near side of his neck