How to load/call .dll files inside C S_function???

Hello,

I have two .dll files which are created by multiple .c++ files. First dll is having Controller action for plant in it. Second dll doing the interfacing action between first dll and plant. Please go through the attached file for entire block diagram.

Now I want to place my S_function block in between second dll and plant(As shown in attached file). If i want to access the signals coming out of second dll inside the matlab environment, I need to call my second dll inside s_function??? So please let me know how to call dll file inside s_function???