How can I handle positional parameters outside main?

I'm using the Poco library to build a server application. One of my command line parameters allows the user to pass the path to a file (-f /path/to/file.ini).

I know I can get the position parameter in virtual int main(const std::vector < std::string > & args); but the documentation clearly states that no threads cannot be created here and I need information present in that configuration file to create threads.

So, how can I access that positional value via an OptionCallback or in the void initialize(Application& self) method?