Hello A., and all,
Here is a proposal using `label` and `goto`, as:
@startuml
:Init;
if (cond 1) then (yes)
:action 1;
detach
elseif (cond 2) then (yes)
label dummy
label dummy
label dummy
label dummy
label a2
:action 2;
detach
elseif (cond 3) then (yes)
:action 3;
if (cond 3-1) then (yes)
label dummy
goto a2
else
:action 3-1;
detach
endif
else
:action 4;
stop
endif
@enduml

It is only on beta version, and not fully operational (with a lot of dummy label!), but: Enjoy,
Regards.