The way that OTRS creates a workflow is with the status. You can create ACLs (in perl) that help you to achieve that. Inside you /opt/otrs/Kernel/Config/files create a new file "MyACL.pm", add these 3 lines:
package Kernel::Config::ACLs;
use strict;
use warnings;
I think it's the best solution to achieve what you want, I did it also like that, but maybe anyone else knows a better way.
Good luck, and don't hesitate to ask for help!
--
Rafa Quiñonero Figuerola
Tlf: 01577-6805709
rafakorp@gmail.com