I remember feeling exactly the same as you OP, not able to accept DC1 as mine, deeply miserable, weepy, hormonal, depressed for the first six months of her life with no let up. Then, things got easier (with some counselling) as I got into a better rhythym, my support networks all clicked into place, and I understood that how I felt was okay. Acceptable, even.
This time, I am planning to sort out all of my support (mum, dad, DH, friends, HV, MW) well in advance. I have kept my counsellor's number on my phone. I am going to discuss my concerns with my GP and HV/MW before I deliver. It might not help me to avoid PND, but it means I won't be looking out for the signs alone. I have also told many friends about what I went through privately last time, so they are aware of how I may be.
Like you, the thought of going through it all again gives me the willies, especially as I have another little person who won't understand 'mummy wants to curl up facing the wall and think about death today' as an excuse for not going on the swings. I have also set my sights on six months after DC2 arrives, rather than focussing so much on the birth. I accept that the first six months may be hell, but I also know that I got through them once, and I hope to do so again.
Don't feel that encapsulation is your only hope. It is an option for some people but remember that millions of women go through PND the world over without making a capsule or smoothie from their placentas first, and come out the other side.
Good luck to you! 