Thank you for your post.
There doesn't seem to be a quick way or setting for this in FileMaker Pro 11.
You might check Setting file options :
Allow Credential Manager to save password (Windows) or Allow Keychain Access to save password(OS X and iOS)
You can prevent users from saving their password by unchecking this option in FileMaker Pro 14.
I hope this helps!
For Windows7, there is a command "cmdkey" to do it (I haven't used it myself), but do your users use standard os feature for storing password? There are many applicatios to do it.