I wouldn't stress too much about it. Even if you can't do it during OLCI for whatever reason, you can still give your number to the check in counter at the airport and have them enter it. The only (slight) disadvantage to this is if you're on a flight that is routinely oversold and they start upgrading *G members prior to check in. I've had that happen on a flight from HKG once (my MileagePlus number was in the res, so they had my *G status), but several other times I've seen them doing the upgrades at the gate instead, by which time they'd have your *G status in the res.