[Zope] Calculated values stored as metadata in ZCatalog?

Hi, Is it possible to store a calculated value as metadata in a ZCatalog? For example, let's say I have a ZClass with properties lastname and firstname, and an external method called "name" which returns "firstname lastname". If I put "name" in the metadata table of the catalog, it looks like the name external method is getting added to the metadata, not the calculated value. Is it possible to get the calculated value in there? (This example is not exactly what I'm doing, but is a fine illustration. I'm trying to avoid waking up the objects to get at this value...) Thanks in advance, Kevin