Now that's a tougher job.
You can get the HES file at various places, like Zophar or my own site. The HES audio format is pretty similar to NSF, it's a ROM stripped of everything that is not music data. Problem is, you can't simply convert it to SMF or some other ringtone format. You'd have to disassemble the ROM, convert the music data down to its original MML format (MML is a simple music writing format in ASCII, which looks like a stylesheet), then convert the MML to SMF.
Some Japanese tools exist for various systems, but I don't think there's anything you can get from the PC Engine right now. You'd better transcript yourself the music by ear on your cellphone