defaults write com.apple.helpviewer NormalWindow -bool true
To turn it in a normal application:
i=/System/Library/CoreServices/"Help Viewer.app"/Contents/Info.plist
sudo defaults write "${i%.plist}" LSUIElement 0
sudo chmod 644 "$i"
defaults write com.apple.helpviewer NormalWindow -bool true
i=/System/Library/CoreServices/"Help Viewer.app"/Contents/Info.plist
sudo defaults write "${i%.plist}" LSUIElement 0
sudo chmod 644 "$i"