I.M Weasel has released an applescript called Mac DC IP.BIN Image Appender that allows Mac OS X users (currently untested for OS 9) to insert an .mr image into an IP.BIN boot file, you can download it from the Mac Needed Tools page. For more info or if you would like to ask I.M Weasel a question about this app you can in this forum topic.

I.M Weasel has also added a guide for selfbooting DCMP3 to his Mac Selfbooting Tutorial, which also has selfbooting guides for DreamSNES, NesterDC, Smeg and StellaDC.