Please allow to use the hide command to hide packages.
Example:
@startuml package util { class util1 } hide util @enduml
(--------)
With last beta: https://dl.dropboxusercontent.com/u/13064071/plantuml.jar you can use the hide command to hide packages.
@startuml class Foo1 class Foo2 hide Foo1 class Foo3 Foo2 *-- Foo3 hide Foo3 package util { class util1 } hide util @enduml
Is this what you are expecting ?