Doing PUTs and GETs with the file payload as a FileStream

What I need to do is to send encrypted files over SFTP using an SSH private key file with the file being delivered in plain text. This needs to be done without creating a temp plain text file on our end. So the flow would be...
***Sending Data***
[Encrypted File] -----+data stream+---> {Encryption Software} ------+data stream+-----> {SFTP Software} ------+SSH data stream+------> [End point File]

***Receiving Data***
[End point File] ------+SSH data stream+------> {SFTP Software} -----+data stream+---> {Encryption Software} ------+data stream+----->[Encrypted File]

I see how you could use StdIn to pass WinSCP a file name but I want to actually send the data stream through StdIn.

Can this be done via WinSCP? If not, is there a free product out there that would?

WinSCP does not support this.