I can think of a way to make it work logically... granted, seems to go the long route, but...

Of course you would have to create a smart contract, right? and the idea would be that when you receive STEEM tokens on the @steemaccountforyouidea you would have a script listening for the transaction.

Then, in theory, once the script receives the transaction, reads the memo, then it would in turn send tokens to the Eth Address on the exchange.

I got that part... makes sense... I do have some considerations regarding the amount, since you technically have to set a hard limit when you create an ERC20 token in quantity, but you could se this stupid high, and it would not be a problem for a long long time, in theory at least.

The way back however, the only way I can think about doing this... is that you would have a script running on a server you run that works as an escrow for the ERC20 token and that generates addresses for every account created on your exchange.

In other words, @meno would have to register on your escrow service, and withdrawals to the Eth address you've given me, thru registration would in turn trigger a transfer from @yourexchangeaccountonhere to the @meno account on the STEEM blockchain.