Ex will not sign MOD

I was approved, on my income ALONE, for an in house MOD through BofA. I bought the house from my EX in 2006 and he quit claimed off the title but his name remains on the original loan. BofA will not process the MOD without BOTH signatures, his and mine, even though he released all liability and has not contributed to the mortgage in OVER 5 years. BofA has accepted the past 4 MOD payments from me although they are now saying it is not approved due to the missing signature.
Is there ANY way to get my EX to sign this MOD or to get BofA to accept the MOD with one signature? Or any way to get EX off mortgage...house is under water+ no equity. My Ex WILL NOT sign and just wants off the loan. My EX and I were never married just together for 10years. BTW, the loan is held by a private investor, not Fannie Mae or Freddie Mac. The home is in California. ANY advice would be GREATLY appreciated. I desperately want to stay in my home!