Firstly - lets establish what size it is that you consider a large sunfish. What size length do you call "runts". Runt sunfish are the prevalent size BG in ponds with too FEW small bass.
Secondly does the pond already have fish in it?
If yes what kinds?
How big is the pond?
Is the pond deep enough to prevent MN winters causing fish winterkill?
Thirdly do you know how to recognize pure stain bluegill compared to hybrid bluegill, green sunfish, and pumpkinseed sunfish????.
Are you getting your stocker sunfish from a fish farm or from a pond or local lake? If any of the stockers are hybrids or mixed sunfish genetics do not expect them or their offspring to do much reproduction. If any of them are hybrids they can reproduce / cross with pure strain bluegill to produce various forms of hybrid sunfish.
As mentioned if you can correctly recognize pure stain BG or get them from a fish farm you could add large adults with the smaller stocker BG. The big trick is to NOT add the first stocker young BG that have been graded at a fish farm as small individuals of the current year class. You want the first stocker BG to be the best and fastest growing ones of that hatch or year class; those are usually best available in fall compared to spring.
The main trick to growing big bluegill is have plenty of small LMB (8"-12") in the pond to eat lot and lots of the baby BG sunfish that are hatched until they are 2 yrs old. This keeps their numbers low density so remaining BG have lots of food for fast growth. BG with overabundant food grow fast to where it takes about 3 years to grow 8" BG in MN. Then expect them to be 0.75"-1 inch larger each year. Also feed the sunfish a high quality high protein fish pellet daily so they always have lots of good quality food for best and fastest growth. Every day that the growing BG do not fill their belly is a day they do not grow. This is where daily feeding fish pellets enhances their growth to be the best they can be for size.
Fourthly - do you know about proper male and female bluegill identification and recognition, and proper BG harvest to produce the biggest and best BG?.
Do some reading and learning from this informative thread about growing big BG from the PBoss Archiveshttps://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=189988#Post189988