I haven't tried it, but a fellow I ran into talked about getting some awesome flavor from toasting coconut from the grocery store. Never having tried either approach, I'm not sure what the difference between using toasted coconut and coconut milk would be. For your substitution for black patent, why not just use roasted barley?
I've also never tried brewing with chocolate, but have read that cocoa nibs or cocoa powder are sometimes added at secondary. The alcohol can at that point draw the chocolate flavors out of the solids. On the other hand, you might try reading this piece, which toys with putting chocolate in at the boil: Brew Your Own: The How-To Homebrew Beer Magazine - Brewing with Chocolate - Ingredients