I'd just convert it to a wav and use a wav editor to cut it into two 40 minute wavs and then encode them to mp3 and burn them. Or you could just clip off the extra time at the end while in wav format. Or you could sacrifice sound quality and encode the mp3 at a lower bitrate but that kind of sucks, unless the MP3 track you have is encoded at something crazy like 224kbps or higher.