Step 1: Acquire Components.
You'll need a few washers, lock-washers, and locknuts, although I'm not going to detail specifically how many and what size you need, since that depends on your bicycle. It's quite simple, just improvise it as you go. I spent about $4 at the hardware store for each of the mounts I'm about to show you, including bolts, nuts, and washers.
Oh, and for the headset-mount, you'll need an old seatpost clamp, salvaged from an old bicycle or perhaps the parts room of your local community bike shop, if you have one.
Step 2: Forward Facing Headset Mount
What you'll want to do is take the bolt out of the seatpost clamp, as it's likely the wrong size for your ball head. Now bend the seatpost clamp open, fit it around your headset, squeeze it back together, and thread your 3/8" bolt through. Ensure you have a lock washer and a regular washer in place first, then the seatpost clamp, then a washer and a locknut on the other side, so it all clamps down tightly and stays tight.
Step 3: Rear-Facing Rack Mount
Unfortunately I wasn't able to find one washer that was simultaneously large enough to make 3 points of contact on my rack, with a 3/8" hole in the center, so I had to stack a small washer onto a larger washer.
So what you want to do here is take your bolt, slip on a lock washer, a small washer, a larger washer, then feed the bolt through some opening on your bike's rack, then the larger washer, the small washer, and a locknut.