Yeah that is something we can do. Currently we only accept orders via a blockchain transaction however we could add an option in the payment screen for copy & pasting a private key (or minikey). Pretty simple to configure the site to import the private key and then perform an internal transaction and report the balance (and confirmations).
I assume having the ability to client to provide a mini private key on the webform would be sufficient to handle most use cases (other than a "traditional" blockchain transfer).
I would love to be able to hand people a casascius coin and should they not want to import it into blockchain.info/wallet then they can always go all blue pill and cashout through fastcash4bitcoins.com
