Previously I used flashmp3player.org which uses a fallback to filename when no ID3v1 or ID3v2 is present (without .mp3 behind it). I checked it out and the function is at the moment in getsongs.php and states that if no ID3 is present it says "Unknown artist". But I hope it can display the filename then otherwise it would be quite unclear which file is which. Other option is to download all songs, ID3 them and re-upload them, but it's quite a hassle.
Previously I used flashmp3player.org which uses a fallback to filename when no ID3v1 or ID3v2 is present (without .mp3 behind it). I checked it out and the function is at the moment in getsongs.php and states that if no ID3 is present it says "Unknown artist". But I hope it can display the filename then otherwise it would be quite unclear which file is which. Other option is to download all songs, ID3 them and re-upload them, but it's quite a hassle.