What they can also do is renegotiate a player to add a fake "likely to be earned" bonus which counts against this year but is not actually earned and thus gets refunded next year, adding to next year's cap. They would have to do this before the last game of the regular season. They could for example give Larry Izzo a 5M bonus for leading the team in interceptions, and all such bonuses negotiated during the season count as "likely", no matter how ridiculous. They have done this before, and there have been no reports that the new CBA changes what they can do in this regard.
Also, Miguel has stated he believes there are up to 2M of "Not Likely To Be Earned" bonues which will actually be earned. If they are, and there is unused cap room at the end of this year they count against it, otherwise they come off our cap next year. So that 6M may well be closer to 4M.