hop back and hot side aeration

Based on my experience, you don't have to worry about oxidation. Whether it's because you pick up so little O2, the fermentation scrubs it, or that HSA worries are overblown, I never encountered any oxidation due to using a hopback. I eventually stopped using one not because of oxidation problems, but because it seemed like a more difficult way to accomplish the same thing I could get from dry hopping.

One option would be to purge the oxygen out of the lines and the hopback using CO2 before you run the wort through. This is a good safety precaution but in my opinion it is not totally necessary since hot side aeration is not a huge issue at Homebrew volumes.

As long as you have a good fermentation, I doubt that this will have a discernable oxidizing effect. The yeast are going to eat any dissolved oxygen in the wort during their reproductive phase (not to mention the fact that you'll be aerating/oxygenating the wort at pitching time).

I suppose if you're really concerned about it, you could dump the first hopback load of wort, and keep the wort that has had less air exposure, but that will also throw out some of the volatile oils and such that you want to get out of the hopback.