Use the cable ties to connect the rubber O-rings together as shown here. Tighten them down as tightly as possible, so that they'll stand straight out. Take care as you're connecting a string of O-rings together to wrap the cable ties in the same direction, so that the spacing between the ties will be uniform.
As you work, keep trying the collar on. When it's about the right length, put the collar around your partner's neck and connect the two ends of the string of O-rings together with a cable tie. That's it! You're done.
Since the rubber O-rings are generally more expensive apiece than the cable ties, I recommend removing the collar by cutting one of the cable ties rather than by cutting an O-ring. A pair of diagonal cutters, tin snips, or strong scissors works well; cut through the base of the cable tie without cutting the O-ring, so that you can put the collar back on again just by using another cable tie.
When you're done, the result will look something like this:
