Has anyone had to develop a matching rule based on a 'partial'
attribute value?

I've got an external database where pk_emEmployee = CN. But (there's
always a but, right?), the pk_emEmployee field is limited to 10
characters. So what I want to be able to do is match back to eDir on
substr(CN,10) and surname.

Any suggestions on how to accomplish this? The 'find matching object'
rule doesn't appear to allow you to parse down the attributes.....