Good question. Right now it is not possible to use the SDK without a position estimate.
I would like to be able to just set the velocity of the drone, without a GPS.
The problem is that you can't control a velocity without a velocity estimate, and you can get a velocity estimate using either a GPS or something like VIO or flow.
If you just want to set the angle of the drone, that's something that we could add to the SDK, however, it means that the drone will drift away slowly (or faster in wind).