There seems like nothing more natural than a good strong soup with some pasta in there to round it out. Here's a couple of tips to make it work.
1. Depending on how you'd like the final product to come out, adjust the water accordingly. If you want the soup to shrink down around the pasta, and form a thick gravy like thing, with the soup ingredients almost ending up as a loose, rich sauce around the pasta, go with about 1 1/2 litres of water per 250 grams of pasta. If you want the pasta to float in the soup, however, amp up the water considerably, because the starches liberated from the surface of the pasta will make the whole thing decidedly more thick.
2. Only use whole wheat pasta. Do /not/ try to use regular white pasta in a soup, because it does not have enough structural integrity to stand up to a long cook (and subsequent soak) in that much liquid. Whole wheat pasta, on the other hand, pretty much won't fall apart. It'll be fine.
3. If you're not serving it immediately, cook the pasta a little on the under-done side. The longer it sits, the more it cooks, and soaks up water. This is why I suggest using whole wheat pasta, because the water won't absorb as well. In other words, try to serve it immediately, but feel free to undercook it if you need to let it park for a bit.
By the by, I generally do not take such a risk, as cooking pasta in soup, where it'll fall apart eventually, but I had some whole wheat pasta (which I ordinarily strongly dislike, but my mother had dropped some off for me), a bunch of soup, and some serious hunger pangs. I didn't have time to bother with rice, which would have taken closer to 20 minutes, so I decided to experiment. If I am combining pasta and soup, I tend to cook the pasta, toss it in a bit of oil and salt and pepper, and serve it on the side with the soup, so that people can combine it in their own bowls to their own liking.