You have some options for drawing vectors:
1) You can use the
starling.display.Canvas class to draw vectors on the GPU. It has some limitations, but it might be worth checking out since it's built into Starling.
2) You can draw your vectors to flash.display.Shape/Sprite, then draw that Shape/Sprite to BitmapData, and upload it as a Texture.
3) You might check out the new draw-lib by @rodrigo. However, he warns that it's still pretty new and not fully optimized that this time that I'm writing this.