Poking around with WinCE P/Invoke...

A few more useful links I found for C# programmers trying to overcome the limitations of interop in the .NET CF:

P/Invoke Arguments [MSDN]

Writing Unmanaged Functions for Microsoft .NET Compact Framework-based Applications [MSDN]  
by Content Master Ltd

Creating a Pocket PC DLL Using C++ [MSDN]

Basically, its time to dust-off your meager C++ skills and hack together a Native wrapper.