Marc,
vbAccelerator ImageList does not implement any overlay image creation techniques, so you need to prepare the required images outside of it and then upload them using one of its standard "AddFrom*" method.
However, after some research, I had one idea of how to do that automatically. But I have not managed to make it work. Maybe, I missed something, so I describe my idea below thinking others can tell me where I was wrong.
First of all, you need to upload your basic images into the standard MSComCtl ImageList OCX (like you do it in your sample). After that you prepare all combinations of your basic images using its Overlay method, but upload them into vbAccelerator ImageList OCX using the AddFromHandle method. The fact is that the MSComctlLib.ImageList.Overlay method returns an OLE Picture object, i.e. an object that implements the IPictureDisp interface. One of the members of IPictureDisp is the Handle property you can use with the vbalImageList.AddFromHandle method. It is also the default property, so I thought the following call should work:
vbalIml.AddFromHandle m_iml.Overlay("doc", "new"), IMAGE_BITMAP
Unfortunately, it just adds the 2nd image specified in the Overlay method ("new" in this sample)...
As a similar idea, you could try to experiment with uploading overlaid images into another temporary store like PictureBox and then uploading them into vbAccelerator image list using one of its methods.