I'm sorry but this is not supported on the RollingSpider. Best thing you can do is, knowing the max tilt (max inclination allowed by the drone), you can know the speed of the drone by experience. Then try to use that speed to make your own flight plan.
For example, let say at a max tilt of 15° you experience that the RollingSpider flies at 5m/s (these values are totally made up). Keeping the same max tilt, if you want it to fly forward for 5 meters, you send it a piloting command of 100% on the pitch axis during 1 second.
This is not accurate at all, but I think it's your only solution.