Would it work to just butt the pieces up against each other and zigzag along the join? Like putting pieces of batting together into a large piece. Or use a fancy zigzag-like stitch if your machine has something like that. Could use contrasting or variegated thread to join blanket pieces together. Haven't tried this myself, but I want to weave some lengths of wool fabric to make a blanket so I will be anxious to see what others suggest!