Lassig, do you still have as your primary goal growing trophy bluegill? If so, I would echo what Dave said, which is that you don't need to create any beds; if you tried to stop the bluegill from spawning you'd be hard-pressed to short of shooting the males one by one with a .22 rifle as they were about to fertilize the eggs. I've never seen a pond that had bluegill in which they didn't spawn successfully, usually without any help at all.
If your goal was trophy bass it would make sense to maximize their spawning success because doing so would lead to more forage for the bass. But if you want to grow the largest bluegill possible, your foremost priority, the most important thing you can do by far, is keeping the bluegill numbers low so the ones that live have more food - just as you would regularly thin out the bass numbers, and aggressively so, if you wanted trophy bass, so you should do everything possible to minimize small bluegill numbers. In a pond that's properly managed this way it's not uncommon for the bluegill to average close to a pound apiece - I've done this more than once, without the benefit of automatic feeders (which I never had a chance to employ until this year).
Fisheries biologists who have studied Lake Ketona in Alabama, which produced the world-record bluegill (T.S. Hudson, 1950) at four pounds twelve ounces, concluded that one of the prime factors in the exceptional growth rate of the bluegill in the lake (the second-biggest on record also came from Ketona, 4 lbs. 10 oz.) was the steep banks that provide the bluegill with very limited spawning areas. The lake also has a large population of small bass, which of course was cited by the biologists as another key factor as the bass eat most of the bluegill at the fry and fingerling stage such that the few that survive have all the food they want, and grow at an unheard-of rate.
Bluegill will spawn on mud, gravel, whatever is available; they prefer gravel substrate; but you don't want to give them what they prefer if you're looking to grow two-pound bluegill. Some bluegill enthusiasts go so far as to stock nothing but male bluegill in a pond, to eliminate spawning altogether. That's probably the surest route to a two-pounder, but the goal is still achievable with a spawning population. But the more you help them spawn, the more you let them do their natural prolific thing, the smaller your bluegill are going to be, automatic feeders or not.
