Or at least there is no option to do so in the Tabular Model Designer in Visual Studio/SSDT. Technically you can set it using AMO, but I would not recommend it (despite AMO being a supported interface, I don't think Microsoft envisioned it being used like this).
A workaround (in the 2012 release) is to create a DAX measure that behaves like IgnoreUnrelatedDimensions=False. An example is provided by Marco Russo here: http://www.sqlbi.com/articles/budget-and-other-data-at-different-granularities-in-powerpivot/ (search the text for "IgnoreUnrelatedDimensions").
Maybe a tabular equivalent to the IgnoreUnrelatedDimensions property will come in a later release.
Please mark correct responses as answers!
- Edited by Christian Wade Thursday, July 11, 2013 9:46 PM