One other option I haven't seen mentioned is this... decide how much wider you want the scarf to be, for example 6". Then knit two strips 3" wide each and make them the length of your finished scarf. (Using two strands of yarn you could probably knit them both on the same needle)
Then either crochet or stitch the strips onto the original length of scarf.
You could use the same needle size and pattern or use a different complimentary pattern for the two strips.
Hope this helps! :o)
In progress - designing, knitting and writing a knitting book, "Design Your Own Gourmet
Kitchen Cloths and Accessories".