Collaboration Services 2.0.1 is shipped with a new mapper that allows for "constructing" the display name of stub objects using any rules or additional attributes. This will help to match display names of objects from other forests to your own GAL appearance rules.
Display Name mapper can be selected on the "Mappers" page of subscription properties. It has five tabs corresponding to all types of objects that QCS can create as a stub. For the needed type of object select check mark "Customize Display Name appearance for objects", click Add Attribute ... and build the template for the object's Display Name. For example, in order to have FirstName.LastName put: