I created my entire keyword set as a text file, using tabs to set the hierarchy. (You have to be really careful using Microsoft Word to do this, since it helpfully changes Tabs to Indents without telling you so. Ask me how I know this....grrrrr)
That text file can then be imported into the keywords panel in Bridge, Photo Mechanic, and, I presume, Lightroom. I use PM, which has a GREAT hierarchical keyword panel -- much easier in my experience than Bridge.