The only person who can file a motion to supress is a party to the criminal action-- namely the defendant.  If the 911 call is relevant to the defendant's defense, then prosecutor is actually required to produce the 911 tape.  Your only realistic option is to talk to the prosecutor on this case, explain your situation, and see if there is something they can do to redact, by agreement, certain portions of the tape that would tip the defendant off about who you were.  This is not a guarantee and rarely happens, but it's your only option... so you'll just need to do what you can to talk to them.