Sorry if this has already been posted, but I didn't find it using search
I have been able to create a custom welcome message on the ftp server.
I had to put a file named .banner in the root. The "." is important.
You may have an issue creating a file that begins with "." in Windows. Just create a simple txt file then go to a DOS prompt and do a rename
rename test.txt .banner
After creating the .banner file you should be able to open it with notepad and make additional changes.
I had a Unix shell account with Netcom back in 1993 :-)