I've mixed fibers with fringe. Just wrap/tie them tog. If you use something that's apt to unravel or fray, once you've trimmed all to the desired length, you can tack the questionable pieces with a bit of Fray Check. (Most ribbons need to be cut on the bias.) Some like to add beads. Just consider that any embellishment be cleaned in a similar fashion. You wouldn't want to work scarf in washable yarn but have a ribbon, or similar, that had to be dry cleaned.
Keeping to the knitting basics