I have read a bit about making hair from greenstuff on dakkadakka, I think. While with the hair you usually put on the GS and make the waves from the blob to give hair, nobody has made dreads yet, but I think a good way would be start like making chain.
Make a GS rope. Decide if you are going to make corn-rows leading into dreads or just individual dreads.
If corn-rows, just place the rope on the forehead of the mini, and gently get it to touch over to the back of the head, and cut it to the length you want. Continue, until you have all your dreads in palce.
Otherwise, take your rope and position it somewhere on the top of the head, and continue going down the side/back/front of the head, until the dread is the right length. Continue around the head until you have your dreads in the right place and some attached to the whole head.
If the GS hasn\'t firmed up too much by this time, you could actually give it a few strands per dread, or make it look like actual rope rather than just a flimsy long cylinder of green stuff.
NOTE: I haven\'t tried this, but would seem the easiest way to do it to me.
Just remember to do the ends of the dreads into the individual hairs a bit so it doesn\'t look like a clear line chopped off when you cut the dread from the rope, but looks more like actual hair.