These things go by many names - Tent adjusters, stay adjusters, line cleats, etc.
To make and use them, follow these directions:
1. Get a 4" x 1" x 1" piece of scrap wood.
2. Drill a 3/8-1/2" hole, 1/2" from either end.
3. Run your rope through one of the holes and tie a big knot so it wont pull back through.
4. Run the tag end of the rope back through the other hole to create a loop.
5. Tie or attach the tag end to your feeder bail handle. Like you, I have an "S" hook on the end I bent from stiff wire. Leave plenty of extra rope beyond the hook to adjust for height.
6. Hang the loop itself from your nail, hook or whatever overhead fixture you are hanging the feeder from.
7. Suspend the feeder from the other end, off the floor, allowing it's weight to pull on the rope. Step back and observe. The cleat should be pulled perpendicular with the floor by the feeders' weight, leaving the cleat tight to the rope.
8. If needed, adjust height of the feeder by grasping the wooden cleat and turning it parallel with the ground. This will free the loop. Adjust the length/size of the loop to get the feeder where you want it. Now release the cleat, so the weight of the feeder pulls the cleat perpendicular to the ground again - thus locking the cleat with the feeder at the desired height.
9. Cut off the excess rope at the bail hook.
If this doesnt help, Ill get a pic.
Here are some rope cleats you can buy, if you want to spend the money. Same principle, fancied up:
http://www.rei.com/product/358151
More fancy, costs more. This you could easily make from hardwood, such as pallet scraps:
http://www.mountainhomemarketing.com/mhm_072807_005.htm
Weren't you ever a Boy Scout?