How to keep billboard parallel with ground like ellipse entity?

I am using BillboardGraphics to show a image which is actually a circle (represents current location). I want this billboard to remain parallel to ground regardless of camera position/orientation like an ellipse entity does. I have tried to use Cesium.Cartesian3.UNIT_Z as alignedAxis but its not what I expected it to be. I can't use ellipse because:
1)A lot of code is already written using BillboardGraphics
2)I am changing position of billboard entity frequently according to my own custom rendering logic. Which I suppose won't work in ellipse entity because it uses callback property to update position. (Correct me if I am wrong)

Can anybody suggest any solution? How to keep the billboard flat/parallel on ground?

I have tried using ellipse with callback property too. It works if changes in position are less frequent. If I change position more frequently then the ellipse won't update.

is this not possible? Can anybody give a slightest hint?

Hi John,

By it’s nature, a billboard will always face the camera, both in Cesium and in most 3D graphics programs.

You can create a circle and keep it parallel to the ground. Will that work for your use case?