This seems to work for me and my BlueTooth Trackpad.

defaults write com.apple.AppleMultitouchTrackpad Clicking -bool true

@athompson When you say that seems to work for you, do you mean it works for you from the command line locally on a machine, or that you're using it in a configuration script to set it globally for all users on a machine? Given the lack of the /Library/Preferences/ prefix on the domain to write the pref to I suspect it's the former, and what I'm looking for is the latter.