Are you familiar with this article by Jeff Moden on grouping islands of contiguous dates?
http://www.sqlservercentral.com/articles/T-SQL/71550/
I believe you can probably use this technique to solve your problem. I confess, I found it somewhat complicated to grasp at first and if I have some available time I may try to apply it directly to your problem.
But I suggest you read it anyway so that even if someone does post a solution that uses it (likely), you understand how it works.
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
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