Custom Schema combining attributes

Hi, Bit of a strange request, but someone may be able to help... We're just busy playing around with [url=http://www.webhelpdesk.com/]WebHelpdesk[/url] from MacsDesign Studio. It includes the capability to hook up to OD, AD and other LDAP directories, but unlike Casper, does not allow us to specify a custom objectClass for LDAP attribute mappings. Whilst this shouldn't normally be a big problem, we also have Kerio's schema extensions installed in our directory and therefore all of our email addresses are stored in the kerio-Mail-Address attribute rather than the EMailAddress attribute. WebHelpdesk only allows us to map attributes to one schema, but I obviously need to map to both Kerio's schema and the Apple standard. I realise I could include the Kerio schema as a part of the Apple one, but this is alreaady deployed and working well and I don't want to mess with it. I wondered therefore whether it is ppossible and if anyone knows how to create a custom schema that references attributes from other schemas? I could then deploy a "WebHelpdesk" schema that includes all the attributes I need and map directly to that. Is it also possible to have the schema append a set value to an attribute? Any pointers much appreciated. Cheers Dan