It may be a longer process than you want to hear about. But heres how I would try to approach it.
Start by trying to get to know him better or atleast start a little better neighbor to neighbor relationship. Keep the fences mended even if the tree hits on his side, or maybe try to watch for people on his property that might not supposed to be there, call him before season and ask how many guys are on his and what they drive becuase you want to keep an eye out for people tresspassing on his yours and the other neighbors; something that you can use for an ice breaker or a reason to talk to the guy a little bit. Just something to mention in passing then you can lead the conversation into the weather or lead it something into his property (ex: hey I see that little creek along our back line is looking dry; how certain type of crops are doing in an area is another great one for a farmer) SOMETHING to get him talking. Dont bring anything to do with QDM up for the first few meetings.
After several conversations, probably over a years time, then start talking to him about his property and start quizing him about the type of people that are hunting it, and the deer they are taking. Lead that conversation into: well do think you could charge more if the quality of deer were better in the area or go into IF YOU leased a chunk of property that you were consistantly killing big bucks on you would want to lease every year. Go on about how 1 group year after year after year would be better for him than multiple groups over multiple years and the pain of finding someone to lease it, and how if it was you'd rather have 1 good group of guys that respect the owners wishes than the possiblity of getting a group that doesnt ect... ect... Then once you get him believing that 1 group of guys that are constantly killing nice deer evey year are gonna wanna continue the lease year after year, THEN lead it into telling him to tell his clients to start a management plan.
NOW.... The flaws with my plan as I see it:
1. If you dont know this guy/dont know where he lives/dont have access to him; its hard to start a conversation.
2. You do have access to him and he doesnt like to talk and you cant start a conversation
3. He is one of those people that could give less than a crap about deer hunting and quality of deer.
4. My plan works great and he tells his clients to not shoot young bucks--you gotta hope they know the difference in a 2.5year 140inch and 7.5year 120inch.
You could always try the 1st meeting sit down: heres the deal buddy I want you to tell your clients its best for everyone if they let young bucks go converstaion....Yea its short sweet and to the point but I dont think your odds are gonna be real great on that.
Lastly remeber once you get him talking: you have TWO ears and ONE mouth. Use them proportionally.