Some info, not really an answer…
The micro-OTG connector accepts either a micro-A connector (in which case the port is a regular port for a host and not a device), or a micro-B connector (in which case an ID pin detects this and switches to device mode). The supplied cable is a micro-B USB cable.
What the device type is is completely up to the programmer. The sample devices (such as mass storage or virtual wired networking) are there because someone created that setup using the kernel’s USB Gadget API and not a full driver.
There are a lot of different devices which can connect via USB, and some use “standardized” generic drivers for their class, while a few have custom drivers. Standard class drivers include devices such as keyboard/mouse (Human Interface Device, or HID), mass storage (such as USB thumb drives), and some other types. If the device itself is one of the “standard” class devices, then probably the Gadget API can be used emulate that device.
If the device is not one of the “standard” class devices, then you cannot use the Gadget API, and must build a full driver yourself.
There isn’t really such a thing as “an Android” gadget, it isn’t a standard class. There are many devices an Android o/s can be used with and pretend to be, e.g., mass storage, but this is generic and would not have Android in its name. You would need to specify much more detail of what you want the port to provide, and unless it is a standard class, then you won’t be able to do this without building a custom driver.