I use Ken's "stuffing method" when I'm doing leg of lamb, with big slivers of fresh garlic and sprigs of fresh rosemary off my plant. GREAT!
ckreef, I've struggled with this issue for a long time, too. I try and grind up my spices as fine as I can first (think dust), then mix into the liquids. However, it can still sometimes clump and clog the injector, if it doesn't emulsify well. For larger cuts, I have a very large needle (about 3/16th" dia), which works great; but I can't use it for small cuts, especially chicken pieces. My smaller one (1/16" dia) is super easy to clog, so I generally stick to liquids (Butchers BBQ chicken marinade/injection works really well and is tasty. I think that they've change the name from Herb and Garlic to Rotisserie?) Or, with some pre-planning, you can soak your herbs and dry spices in liquid for a week to make a tincture that will inject easier. You have to really amp up the amount of herbs/spices if you try this, as you can't get a very good extraction easily and remember to shake it up several times a day, as most things will settle to the bottom of the jar. Plus, some things are water soluble, others in alcohol, still others in acids (wine, vinegar). So, finding the happy medium is a challenge. If you come up with something that works well, I'm all ears!!!