When calling virtual methods the actual function address is looked up in the virtual function table. You register the virtual methods in exactly the same way as normal non-virtual class methods using the asCALL_THISCALL calling convention. AngelScript automatically detects if the method is virtual or non-virtual by inspecting the method pointer received in the RegisterObjectMethod call.

Even when dynamically loading COM objects you have the interface definition for the objects at compile time, so you should register the methods from that interface.

Or are you somehow dynamically determining the C++ interface too at runtime? If so, I imagine you could define a dummy interface with several virtual methods, one for each function table index. And then register the method pointers from that dummy interface instead, thus having a valid virtual method pointer.

Alternatively you could do something more hardcoded and construct the virtual method pointer manually. But then you'll have to make sure you the deal with the platform differences, as each compiler/platform can use different structures to represent virtual method pointers.

Let me know how it goes. And if you can share some code on how you dynamically determine the function and index it would be great. Perhaps I can add an article in the manual for how to register COM objects with the engine if you show me how it can be done.