Temporarily protect array from garbage collection

[Lars T. Kyllingstad via Digitalmars-d-learn]

Is it possible to temporarily prevent the garbage collector from 
collecting a memory block even if there are no references to it?

The use case is as follows:  I want to call a C library function 
which expects to take ownership of a buffer.  It looks something 
like this:

     alias FreeFunc = extern(C) void function(void*, void*) 
nothrow;

     extern(C) void foo(void* buf, size_t len,
                        FreeFunc free, void* ctx) nothrow;

Here, 'buf' is a pointer to the buffer, 'len' is the length of 
the buffer, 'free' is a function to deallocate the buffer when 
the library is done with it, and 'ctx' is a user-supplied context 
pointer.  Upon deallocation, 'free' receives two parameters; the 
pointer to the buffer and the context pointer.  The latter can be 
anything, even null, as it is just passed to 'free' and not used 
for anything else.

Here is the problem:  I want to be able to use a 
garbage-collected dynamic array with this function, but I don't 
want to have to retain a reference to it in my program.  (I don't 
know when the C library will call the free function.)  In other 
words, I want something like this:

     extern(C) void myFree(void* ptr, void* ctx)
     {
         enableGCFor(ptr);
     }

     auto arr = new int[123];
     disableGCFor(arr);
     foo(arr.ptr, arr.length, &myFree, null);
     arr = null;

Is this at all possible?

Thanks,
Lars