Hi all,
From:
@startuml
|swimlane 1|
start
repeat
|swimlane 2|
:read data;
|swimlane 1|
:generate diagrams;
repeat while (more data?)
stop
@enduml

You can add a dummy label and obtain:
@startuml
|swimlane 1|
start
repeat
label dummylab
|swimlane 2|
:read data;
|swimlane 1|
:generate diagrams;
repeat while (more data?)
stop
@enduml

Enjoy,
Regards,
Th.