I don't think that there is absolute way of eliminating multi's for equal distribution. Exchange airdop probably will not solve it. What I think is to reward community and eliminating multi's, set a specific date like 10 April than qualify all users under this topic who messaged to topic till the specified date.
I think the best approach to eliminate fraud is to make the airdrop based on the SIRX holding of an individual. Most cheaters already sold their coins so they're chance of getting back to airdrop is none unless they bought back from the market.
I agree... Multi accounts won't work if you airdrop in ratio to its holding. This should be the best away.