I don't know for sure (I don't have much experience with DLLs yet) but I guess you just have to create a standard DLL in C++, like you would any other DLL.
To access it, call "Load DLL" (DBPro checks the system32 windows folder and the exe directory first, so no relative pathnames are needed). To call functions from the dll, just use "Call DLL". I'm not sure if you'd need the decorated function names or not.
Just out of interest, why wouldn't you wnt your DLL to be a full-fledged plugin? There's so much work going into making a DLL anyway, it's not that much more to make it a compatible plugin.
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