I've worn a clip-on uniform tie my whole airline career - wouldn't be caught dead out of uniform with one on, though. The nanosecond the cockpit door closes that bad boy gets taken off. If you loosen up a regular tie on every leg, then they get pilly and worn out in a matter of weeks. I'll second Smoking Man's advice about having a noose around your neck in the event of a throw down, as well.
If you buy a cheap clip-on, you can carefully take it apart and see how it goes together. Take your regular tie (I'd suggest a long one, as this method eats up a lot of length) and wrap it around the little plastic thingee that has the clip on it. It might take a couple of tries to get the ends the right length. Sew the sides together and presto, clip-on tie.