I tried to copy Susan V's Black Bean Hummus spiderweb. I failed miserably. Tahini doesn't like being in a pastry bag. Who'da thunk?
The recipe is here if you're still looking for something to spook-ify the big day tomorrow. I suggest taking her up on the soy yogurt option, which I didn't do because I didn't have any, but I think it would bring the flavour together a bit more. Plus it is more likely to cooperate with you when you are piping the spiderweb.