I discussed this scenario once with a trainer and I think it shows good airmanship to consider it.
You need the 30 mins above FL300 to get rid of the cavitation but after that you can do gravity feeding. Just realise that you will create an imbalance of about 1200+ kg and that when you arrive at destination you could end up with only a few hundered kilo's on the positive pressure side. Depending of course on how much extra you took.