LDAP setup in root (mngmt) vdom. How can I get my 2nd VDOM to use that LDAP?

I've setup my Fortigate using two VDOMs:

1) Root (management)

2) WEB-FILTER (Transparent)

Due to the WEB-FILTER being setup as transparent I've setup access and the LDAP server in the root VDOM. 

Now I want the WEB-FILTER VDOM to be able to authenticate users (for web filtering) using the LDAP group setup in the ROOT vdom. I can't seem to get this to work however.  Is there an easy way for me to just use the LDAP details already setup in the root VDOM?

Thanks