Well, since there are cap holds for empty roster spots, the only way to do this would be (I'll spare the math):
1: A sign-and-trade that gets rid of Beasley
2: Wade, LeBron, and Bosh each accept a contract starting (at an average, so one guy could be higher and two lower) under $14.9M, instead of the over $16.5M starting salary they can get now.
That leaves enough cap room for a contract starting at $5M for Miller.
The team would be: LeBron, Wade, Bosh, Miller, Chalmers, and 8 guys signed at the veteran's minimum (or their second round picks...also at minimum salary I think).