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We have a wallet address, so we should be able to transfer Steem in from any exchange using the public key, but I am unsure which private key to use. Probably the same wallet address that block trades uses when you buy Dteem from them.

https://steemit.com/steem/@cryptos/how-to-transfer-steem-from-poloniex-to-steemit-com
I think you would save like 10% if you did direct transfers.
Not sure if this would work.