I will try to have here the modified ramdisk images of the various Mageia Live releases so that you can boot Mageia Live off an EXT4 USB partition.
Please note that I am naming those images as mga?init32 and mga?init64, where ? reflects the Mageia release.
Should you need any help on how to prepare your USB, please visit The Mageia Forum Howto on this subject. If you still have doubts, please feel free to email me *_*.
Have fun and enjoy it!