It's pretty easy to make a premine transparent if you really want to do so. Don't shift coins around and post on your website a ledger of all the withdrawals/transfers with transaction ids and purpose (linking to giveaway threads for instance). You could dump most of that info out of the wallet so it would really only take an hour or two to setup. Once all your books were completely public I think most people would shut up about the premine and your coin would even be seen as setting a new standard in transparency and professionalism.

Actually you could do this in 5 minutes if you're worried about the effort. Click on the export transactions button in the wallet or wallets holding all the premined coins and post that CSV file along with links to the threads where you did giveaways or bounties. Put up a modest bounty for organizing this into a readable, semi-pretty form and you're done. This will give your coin an innovative feature (transparent premine) to set it apart from the rest. Even if the devs are planning on taking some of it later I don't think people would flip out as much if it were transparently done at a later date (so that people know that you have incentive to keep developing and not abandon the coin).