If anyone is interested, I'll be happy to make it available as a free tool.
I've tested it with Greek and Cyrillic (UNICODE) tracks, and it seems to work.
It seems to work on most of my M3U playlists (using MMJB), but it's a quick and dirty converter, so I don't currently check for things like unterminated quotes, quoted strings, and so on. It takes an M3U playlist file and converts the track list to the ImgBurn. I've just written a small M3U to CUE file converter.