GC and multiple inheritance as in C++

Hello, I have a question concerning implementation of multiple inheritance in CIL. For a C++ MI object, a pointer can points to inside the object body instead of the its head. eg.
struct A : B, C { };  C* c = new A;
While Boehm GC detects this kind of reference, is it a supported feature of Mono? If not, what is the suggested way to implement it (eg. what is the C++/CLI way) ?

Thanks you