What about cotton plates? You can put silicon in some holes to drop less seed. Our cotton plates were 4 drop hill drop plates and we stopped  up two of the holes to just drop two seeds per drop. Sorry I just noticed you said 7100 so not vacuum planter. Someone should have a set of sunflower plates you could use. I planted a few one time but don't remember what I used. As well as I remember not that many seed per ac.