Ok, generally the commercial injects use xanthan gum to thicken them, which I assume would be to hold them in place a bit longer and like you stated: less prone to leaking out. Xanthan gum is packaged be Bob's Red Mill and can be found in supermarkets that stock that line. It's pretty pricey, but you end up buying a lifetime supply. It can be a bit clumpy when hydrated, so I generally make my inject, strain it well, dissolve the xanthan, then puree it with a stick blender. I don't blame you if you don't want to go that route, I only tried it because I wanted to try to fabricate my own version of Butcher's inject.
I'm wondering if jelly might be a better option than sauce. The jelly will melt during cooking and the pectin might give you a finish like the gelatin that comes from the breakdown of collagen.
With pulled pork, I lean towards adding flavors towards the end with a sauce, rather than up front with an inject. Most flavors don't hold up to long cooking and are generally undetectable in the finished product. Consider mix 1/3 apple jelly with 2/3 bbq sauce and glaze the butt with it during the last 60 min or so.
