Well, I've found this area. Custom HTTPD Configurations. This is not working, though:
EDIT: I have this working now, but it adds my code to /usr/local/directadmin/data/users/admin/openlitespeed.conf which states at the top:
"# Auto generated openlitespeed config file by DirectAdmin version 1.59.5
# Modifying this file is not recommended as any changes you make will be
# overwritten when the user makes any changes to their website"