How much of the optimisation is done in Sketchup and how much is done manually? Haven't touched Sketchup for a very long time. For stuff like this I tend to use the linear calculator here - http://workshop-buddy.com/cut-optimization-calculator.html
The optimisation is all mine but I set the guide lines to be the length of existing stock and model the required cuts. Then I just rearrange them until they fit with the least possible waste. In this example it should be obvious the most efficient cut must be in pairs. That helped quite a bit. I also ran back out to double check my measurements because I recall leaving them long (just in case).
The web calculator you linked to couldn't do it. Might be a Mac thing but it just says can't fit...