One of the great things about tea (or in this case, tisanes) is that it is highly flexible in how you prepare it. Originally when I started drinking tea, I was interested in buying it in all of its flavored varieties. I have since strayed away from that thought considerably. Instead, you can pretty much drop any spice, fruit, etc. into the infuser with the tea or tisane to add its flavor. I have found that you don't really have to coat the tea in your additive, rather it just needs to be present in the infuser.
So you can take cloves, cinnamon sticks, dried fruit, ginger root, and whatever else, grind it up a little in a pestle and mortar, and toss it in with the rooibos. It works well, in my experience. And this way, you can adjust to taste. Too weak? Add more!