Ok I figured this out, and it turned out to be similar to what I had to do for styles in some ways.
The answer someone posted on this forum post got me started:
http://social.msdn.microsoft.com/Forums/is/oxmlsdk/thread/7d55514b-f846-4790-b545-3693ab18d966[
^]
I took the xml in his answer and made it into an xml file in my project. I then set that to copy always in its properties. After doing that, I use the following function to add the settings to the document, and it will open correctly for Word 2010:
private static void AddSettingsToMainDocumentPart(MainDocumentPart part)
{
DocumentSettingsPart settingsPart = part.AddNewPart<DocumentSettingsPart>();
FileStream settingsTemplate = new FileStream("settings.xml", FileMode.Open, FileAccess.Read);
settingsPart.FeedData(settingsTemplate);
settingsPart.Settings.Save();
}
Doing that has made it so my documents open without being in compatibility mode.