You might like to check out one of the new features due out in Copter 3.5:
Here's a video of it in action: https://www.youtube.com/watch?v=hDzkp2Kfdt4
That's a fully autonomous mission.
Now that feature is currently purely based on throttle-output required to maintain hover (or descent rate). If your vehicle is as heavy as mine, then putting a golf ball on the ground may not make a sufficient difference to the thrust requirements to be above the "noise threshold" that must be present for gusts of wind and the like.
You can try it and see how it goes - but some other mechanism for determining that the "package" has been placed is not unreasonable - a switch ("button" in ardupilot parlance), perhaps.
Also, currently we only compile in support for a single gripper,. That is relatively easily changed. It may also be possible to develop a ball release mechanism which drops one ball when the servo signal indicated a "release" should occur.