Hmmm... let's see.... See you can take COBing like informal rush, and still have those little parties and stuff with the themes. You can have a lil "garden party" theme after the BBQ, where you can have those lil veggie platters, etc and have your excellence binder out or facts or something on a table that they can flip through. We made a video about the things we do year round so that they can get the idea that we are serious about what we do, but have fun at the same time... (i think i love that video because of all the songs in it and hate the video since it has pics of me making a fool outta myself on the dance floor).
You can also invite girls to just chill with sisters, not at the house or anything like that because that might be a bit intimidating, but to the movies, dinner at the local hang out, wherever the PNM won't feel more uncomfy than she is already. Remember that the goal is to get the PNM relaxed and talking so that you can find our more about her, the PNM can find out more about you and the sorority, and to see if she'd meet the reqs of being Phi Sig.