Search People ONLY on some metadata Properties and with Wildcard

Hi, 

   I need to perform a People search, only on SOME metadataproperties, and with wildcard prefixe.

   The Query would be somehow this: "FirstName:key* OR Department:key* OR JobTitle:key*"

   I can do such querys, for common search, extending the Core Search Results Web Part, and overriding theQueryManager, UserQuery property. But Search People Core Results class is sealde, so i cannot extending it.

   Do you have any ideas, please ?

Best regards !

Marco