Like I said, I don't know how much difference it would make...but it is regular practice for many to flush bottles, kegs, lines, filters, etc with CO2 before using them. I think I would be more concerned about the O2 in the head space and dissolving since the CO2 isn't going to push it out very fast since it will get all swirled up during the bubbling. It would be interesting to let it bubble up through and then take a match or lighter or something and put it down into the headspace at 1 minute intervals to see how long it takes for it to settle out. I regularly use the lighter/match test to see if have a good CO2 flush on my kegs and it seems to work pretty well.