There is an absolutely wonderful graph presentation from last year's summit by Vicky L. that shows how to do exactly what you want. You can find it here: http://www.informationbuilders...tml?code=36&code2=43 Look for "Complex Business Graphs Made Simple".
Basically the idea is to make each of the end points its own series on the graph. I showed this to my business users and they were very excited by the concept. It is very clever. Check it out as I think it will solve your problem.