In that case, since you say that soul reaper is being the problem, you should look to rotate external cooldowns. A prot paladin only has one strong personal defensive - Divine Protection. You can use that one to soak one soul reaper in its entirety, since its a hard cooldown. For the other ones you will need to call out Pain Supression and Hand of Sacrifice or Intervene, but with Hand of Sacrifice, which can run out and most likely will (as you've found out), you might need your healer to pop a throughoutput cooldown as well, or kite a bit if he doesn't have one. If you're using heroism throughout P2, you could try simply kiting for the duration of soul reaper and rely on your healers to just overheal.
If you have nothing available, you can use an Ardent proc.