How to hook a MetaTrader custom function into DLL

Hello,
i have a DLL which can make use of callback functions. This custom function is called from
DLL on specific events. The callback function must be of stdcall and is of type void.

->
static void stdcall CallBackF(string var,double var2,int var3).

The DLL function to hook a cb is then called like this:
HookMyFunction((int) CallBackF); // only for 32 bit processes (int) CallBackF points entry of callback

Now i need to know, if MetaTrader at all can provide such a callback function
and how to declare it that it is static and how get its pointer ?

thank you