Hi my name is christian i am a webmaster with [link moderated] 🙂 have you tried a php script that generates the subdirectory manually from the outside like this sample
http://www.hotrockhosting.com/test/make-dir/
here is the code it is in 2 parts.
1 Html page & 1 PHP page
html post the variable to the php which in turns runs the create subdirectory command in the cpanel
[Code moderated as per the Forum Rules. Please use the pastebin]
hope this helps if ya want to email me with questions send email to webdesignerchristian @ gmail.com