Yes, it's simple enough once you know how (most computer things are simple, they're just also
obscure 
).
What you do is log into the account that you want to de-authorize from (through the Sony software). Connect your Reader, and go to the "Account" page. On that page, over in the left column of the main window you'll see a "Manage Devices." Under that you'll see the devices registered to the account, that should let you de-auth the Reader from there.
