He has two means of doing this. First, he can convert the oligarchs from businessmen into members of the apparatus. Most came from the apparatus, after all. And within it they can enjoy the power and privileges of the state elite, while keeping their cash buried in foreign banks. Russian history is replete with examples of the elite changing sides.
Class hatred runs deep in Russia.
The one thing that can frighten the oligarchs is a massive outpouring of anger from the masses, now apathetic. The traditional communist calls tend not to move people these days. Putin has done everything possible to revive Russian nationalism and create an image of himself as the owner of and spokesman for the Russian national interest. Chechnya was critical, a case study in how he would halt the disintegration of the Russian Federation. Much of his popularity depends on nationalism.