IDataObject and COM Interop

I have a .NET IDataObject which contains some virtual file information. 

This all works fine and dandy in that I can use it in a drag-and-drop
process and let the user drop into a Windows Explorer folder.
I can also put it on the clipboard and let the user paste into a Windows
Explorer folder.
In both cases, I get a callback to stream the files and the OS takes
care of displaying the copy dialogue and copes with existing files etc.

What I would like to do is be able to 'force' a drop/paste (preferable a
drop since the clipboard can then be left as-is) directly into a named
folder.

I have managed to crib some code from a CodeProject article to use the
ShellFolder API to call GetUIObjectOf on the target folder and then get
a reference to IDropTarget and then call IDropTarget.DragDrop with a
pointer to a IDataObject (the COM interface one) and this seems to work
fine thus proving it can be done in theory. 

However in my test code, to get a COM IDataObject I was using
OleGetClipboard to get a 'real' COM IDataObject created by the article
app. I could not get it to work where the clipboard contents were set in
.NET code (AccessViolationException - Attempted to read or write
protected memory).

Is it possible to get a real COM IDataObject pointer from a .NET
IDataObject object and keep it pinned/ref-counted or whatever so that I
can pass it to an external API?

Cheers
Simon

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