I'm not even sure if you need to have BitcoinGold Core fully synced to be able to create the transaction or not... Have you tried doing it now while you wait for the sync to complete? There is no harm in trying to create the raw transaction... at worst it just won't work.

The only downside to not syncing, is that if you use a BTG receive address generated by your copy of BitcoinGold Core, you won't be able to see your coins until it is fully synced... but you can create the transaction to send to any BTG address, it doesn't have to be from your copy of BTG Core, so you can send to an exchange address etc.