Not sure how accurate this is but it https://www.steem.center/index.php?title=Reward_Beneficiary mentions that it came in with hardfork 18, maybe now that it is here they can add an update to make the option for liquid but I won't hold my breath on anything Steem and definitely just take this as "Hey always remember."

Or someone sets up an account that always has liquid on hand and they can serve as the exchange, check the original post when payout maybe we state these are the beneficiaries, match with payout received and the exchange makes the payout less maybe a little, for obvious reasons they can take even less for whitelisted charities.