I tried it on a small scale this year. In the spring I disked up an area about 8 feet wide and 100 feet long, covered it with a layer of manure, and disked that in maybe ten times over the course of a couple of weeks. When the weather got warm enough I planted three rows of sunflowers (I bought a package of 1000 seeds: Sun 3703 from Johnny's Seeds).
The first time I checked on them, I saw some sunflower seed hulls here and there where the birds had apparently dug up some of my seeds. "Ho, ho" , said I, "those rascally birds got a few of my seeds. Oh well, lots are left in the ground."
We got some nice rain and the plants started popping up. It was fun, except I noticed that a few of the new plants had been chewed off, and a few had been pulled out of the ground. "Hmmmm, must be those pesky rabbits", I said, "Oh well, lots more plants are coming up."
It kept going like that for the next few weeks, and eventually the critters ate every sunflower plant and now I have none. Sorry. I'm sure you were hoping for a success story. I suppose if I had planted a few acres, I would have had a lot of survivors.
In my area, some folks do plant whole fields of sunflowers, and they do look pretty impressive. On a small scale like mine, I guess I'll have to fence it in next time.
Good luck with yours, if you decide to do it.
Tom