What I generally do is build one or two elements at a time, and see if they meet at a point after those elements. Following that I build track back to the station to see if the timing is right. Granted, you need cash to be able to do this, but I usually get good results.
I've got a dueling ride here:
http://www.coasterbuzz.com/BuzzPlanet.zip (Requires Drexler patch, CF and access to Mega Park scenario.)
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Jeff
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