Create virtual devices (slave mode)

I need to find out a way to develop an app that creates two virtual devices on the serial port but still in usb slave mode. Here is what I need to do:

Install my app on android.
Connect my android via usb cable to a Windows CE host.
Windows CE will detect two devices:
1. USB MASS STORAGE (android app will map this to a fs image file - can be readonly)
2. Standard serial port (android app will read and write to this port to communicate to a specific app on WinCE).

Is there any APIs that helps me to do this? I can only find docs about USB HOST mode and thats not what I'm looking for.