Here is another article that may have the solution you want. It is much more technical and actually tells how to use Excel's XSLT style sheet feature to achieve the result, not anything in SSRS per se. It doesn't seem to be particularly easy to set up, but once you have the XSLT document prepared and have practiced the process once or twice, I think it would not be a huge undertaking to do it each time you run the report.
This technique is listed as workable for SSRS 2005, so I assume it would work with 2008 as well. It might even work with SSRS 2008 R2, though it would be much easier to use the built-in option after you upgrade to that version.