Facading Azure storage blob with sFTP service
You could possibly achieve this by simply exposing the blob storage endpoints directly over HTTPS and look to use Shared Access Signatures (http://www.windowsazure.com/en-us/documentation/articles/storage-dotnet-shared-access-signature-part-1/) to restrict access to those blobs.
Based on your feedback then - perhaps look to leverage Linux to run an sFTP server and use either the Java, Node or PHP Azure SDKs to achieve the same objective of pulling your content from blob storage on a scheduled basis without the need of a worker role (cron should see you right). To be honest you'll be doubling your storage use (not that it's that expensive) as you'll pull the blob out of storage and onto the VHD of your VM but this approach would work.
I notice you said you were encrypting the files written to blob storage - you could just use a PKI approach and share the key with customers allowing them to pull directly via HTTPS. Anyway, sFTP it appears to be :).