[Exim] using/calling 'system_filter' from local_scan

Is there any way to simply use 'system_filter' from local_scan?
At least, any pointer about how to call the function(s) needed
inside local_scan would be appreciated, of course if the available
for local_scan.

Of course I could build my own, but I prefer to use native exim
format without re-inventing the wheel.

Hope that I'm not asking the wrong question (yeah .. I'm totally
exim newbie) :-)

Thank you.

Regards,

P.Y. Adi Prasaja