OK...what I called a 'splash screen', is the display that says: Login at the top, with "New", "Load", "Save", etc. along the right pane.
Maybe I'm wrong, but "splash screen" is AFAIK used for those images shown when some application is starting (like MS Word has).
Anyway there's currently no way for you to modify the login dialog easily.
If you want I can send you "translation file" that would "translate" only title of the login window to display some custom text. But it will work only for the current version and I'm not going to update it for you for each new version.
You may also put the text into name of the stored session like "Double-click me to login to OurCompany FTP"