Once you make a play-list, you should be able to pick up your song (just like a Mii in Mii-Channel) and put it everywhere in list.
Another solution is simpler: build 2 arrows, UP and DOWN, to make the selected song go up or down in the list.

Ok, end of this suggestion: I follow WiiMC by months and I think it’s simply wonderful. Compliments guys, maybe one day I’ll be able to program something for Wii and I’ll guve you a hand for this project.