Hi Mikael,
You can do it by writing code in the metadata browse and resolve methods that gives you a Put method to call.
The LOB adapter SDK seems to me more focussed on LOB systems that expose metadata. You can look at using a custom WCF channel for SFTP, but there is no help from the wizard here.
The Adapter SDN could relly benifit form having a wizard for creating proticol adapters as well as metadata driven adapters.
Regards,
Alan