IMO it has been a non-issue. I cold crash in the same place I fermented, I'm not sloshing the beer around, so while oxygen may be getting into the fermenter, I don't think it's mixing much with the beer. I guess if I get "oxydation" feedback from the Spring Swap or from my brew club, I'll take a harder look at it, but for now: no oxydation notes and no worries.
If I'm using a 3 piece airlock, I simply remove the inside water lock, and cover the lid with a bit of foil. If I'm using an S-lock, I just crash it in place.