Just a small comment, I think that the current vanilla en_US dict is a bit weak for this use case and that perhaps the use of the OOo? dict would be better, this supports em/en dash as well as typographic apostrophes.
Converting the current one is possible, however I got a bit annoyed with figuring it out and just tried out the one from :
http://extensions.services.openoffic.../dict-en-fixed (open as zip, includes GB and others, tho their support is a bit lacking)
There might be newer versions which are a bit more expansive, I havent looked in the official repo.
Which has worked quite a lot better and surpassed my use-case.