They're cheap enough, cut the blade off of a P4 squirt or grind a bluntness on the S4's scissors while you are at it. Try to get it a different color than the real one that you have in your checked baggage, and put a note in your bag to remind you to make the swap, and maybe a sticky note on your ticket.

Or go with any of the knock offs that you can get for like ten bucks at a big chain.