A new feature that has been added recently is connector. Right now, this is really basic, you can just have :
@startuml
:start;
(A)
:other stuff;
@enduml
Maybe it can be a workaround to function call ?
We are open to suggestion about a extended syntax. You can also draw (using some image editor) a simple example of what you are expecting, it may help us.
Regards,