As a temporary measure can you at least do following :
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- Only people with 0 hbc coins can buy hbc coins
- Set limit to maximum 100 coins per user.

This way people can buy 100 coins and withdraw their btc if they want to and all the complaining will stop and hbc can proceed with their plan.

There are people who have deposited funds before start of first sale - let them at least buy 100 coins.

Once again I'll write, the only way out is for everyone who has btc to make an automatic change of btc to 100 hbc.
Thus, anyone who believes in your project will receive the minimum amount of coins and then decide whether to play this game or deduce the rest of the money before the fork.