By paying them.
So we're recruiting Thomas Bryant, for example. Let's say his top three teams are Ohio State, Syracuse, and Seton Hall.
Ohio State offers:
1st year: 1.1M, 2nd year: 1.3M, 3rd year: 1.5M, 4th year: 1.7M
Full scholarship (obviously included, it's like signing an NBA player and telling him he has to pay a membership to play for the team. You begin to see how nonsense the "scholarship is priceless" logic is in economic terms.)
Off campus house
100k signing bonus/Buyout clause
Syracuse offers:
1st year: 1M, 2nd year: 1.5M, 3rd year: 2.0M, 4th year: 2.5M
Full scholarship
Off campus house
75K signing bonus/Buyout clause
Seton Hall offers:
1st year: 500k, 2nd year: 750k, 3rd year: 1M, 4th year: 1.25M
Full scholarship
Off campus house
50K signing bonus/Buyout clause
All price increases are dependent on pre-agreed achievements (minutes played, points, awards, etc.). If a player has injury issues or does not turn out like expected (Dajuan Coleman), they can be bought out of their contract for a price and are free to join another college team while they are eligible, or jump to the professional ranks. Most likely they will sign with a college team.
They are receiving money right away. There is no more jumping to the NBA to "get mom out of the bad neighborhood". Jerami Grant is not leaving this year to help his family's financial problems, since he would be getting paid at Syracuse. Players are getting paid while they are developing. Now on to the big stars:
Tyler Ennis
Let's say his freshman year he had a contract for 450k and was due 650k for his sophmore year. Let's say he outplayed it and is now looking for top college PG money, which will be on par with the NBA rookie wage scale. Let's say Ennis is projected to go between 12th-18th in the draft. The wage scale for those draft positions ranges from 1.2M-1.6M. Now Syracuse has the leverage to offer him a new contract with increased pay on par with the NBA. Why in the world would Tyler Ennis leave now?
Wiggins, Randle, Embiid, and Smart would all stay 2-4 years. They would jump into the NBA Larry Bird/Magic Johnson/Michael Jordan style with 4 years of college experience behind their belt. The "College lifestyle" for these players would be similar to the "NBA lifestyle". Money, groupies, partying, cars, houses. Why the rush to jump to the NBA? CJ Fair wouldn't have even thought about the NBA after his Junior year. For most players, this is the most money they will earn in their lives.
The main reasons I could see the very top players leaving early is that an NBA contract gives them a jump start to their 2nd NBA contract which is where the SERIOUS money is. So now we are talking about only the VERY ELITE players at risk to leave, rather than any good player with NBA potential. But in a free economy, teams like Kentucky or Duke can counter--act this by offering contracts high above the NBA rookie wage scale. If this forces the NBA to raise the rookie wage scale, WELL WELL WELL, turns out these players are worth more than they are paying them.
The NCAA loves to talk about how most of these college athletes never go pro. That's completely true. How many college football and basketball stars can you remember that graced magazine covers in college and then went undrafted or flamed out in 1-2 years? They may have been worth millions of dollars to the university for those 1-4 years but didn't get a penny. They never have a chance to earn that kind of money again in their lives. This way, they may never make the pros, but they'll still get what the market says they deserve for at least a short while.
I'll leave you with this little history lesson:
Look into the Plan B free agency the NFL had between 1987-1992 that restricted player movement between teams. During the anti-trust lawsuit against the NFL, the NFL lawyer was quoted as saying that "Ending Plan B free agency may be the destruction of the NFL". Pure fear-mongering by the corporate institution in order to keep wage leverage in their favor. Sound familiar?
Not only will paying players NOT ruin college basketball, it will IMPROVE the game by keeping the best players around most of their college careers.