It's not working for object, but for class you can have :
@startuml
hide CircledCharacter
class foo {
dummy1
--
dummy2
}
@enduml
http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuSh8J4bLSCuiIiv9JN7EI2nAJ2v9BU9ApaaiBbP8oyzNgEPAAStDhJJaqjM5i8ouQhaSKlE0x1m0