Access Matlab System object instance from Simulink callback

Hi,

I have a functional class, named say "fClass", inheriting from the matlab.System class. When inserted to Simulink as a MATLAB System block, as say a block "mSysBlock", I'd like to call methods from fClass on the object instance that is assumably created for the block. Is there a way to access the system object instance of mSysBlock? When is the instance created, i.e. which callback can already access it?

Thank you, Jiri