It wouldn't be possible because UA's SDK also generates something called an APID to use as a unique identifier on Android, which is stored device-side to enable push notifications. The APID is used by UA for all interactions with the device.
That's why also no server-side method exists for creating APIDs.
The SDK will be the best route. It's actually a pretty straightforward, simple integration, though: http://docs.urbanairship.com/build/android.html
Cheers, -B