Let me see if I'm getting this picture right. You need a flat braid 4 inches long by a 1/2 inch wide? Correct?
Then you need to go back to a 4 strand round braid? Correct?
How's this all going to come together at the point of the round braiding? Is this one of those leads you put through a loop, like a cinch type lead, or something else you have in mind?
I would consider doing a 6 strand flat braid and then dropping enough strands to do your 4 strand round braids.
Brian...