The convicted mastermind of a $100 million mortgage scam was charged Thursday with plotting from prison to whack the  “rat” who testified against him. Aaron Hand is accused of turning to his parents and friends for money so he could hire a hitman for $2,000 to kill the witness who helped put him behind bars. Hand was taped giving instuctions to the “hitman” –  actually an investigator from the Manhattan District Attorney’s Office –  on how to shoot the witness, his wife and their two kids at their home in Brooklyn and dump the bodies. “No samples, no DNA, no gloves,” Hand said, according to court papers. “Wear something over your head.”