Cannot. This is from the s6 docs. I'm not using s6. Just heard about it today.
Another s6 limitation - finish script must end in 3 seconds. or will be killed.
Nice for desktop, not a server.
It used to be that an application is responsible for proper start
up/shutdown procedure, as application knows the proper way how to do
it. Init script is just a place where to hook a startup/shutdown
script to be executed when system needs to start/stop application in
some automatic way.

Now there are tools which help deamonize things.
Depending how portable they are it make the price one has to pay when
decides to use them instead of handling this yourself in the
application.

Regards
piotr