Adding more widgets in 'Widget' Lock screen style of HTC One X I have HTC One X with Android 4.2.2 and Sense 5. 

In 'Settings > Personalize > Lock screen style > Widget' when I click on 'Settings' button I have options of Gmail, Google Now, Google+ posts, My Tracks, Tumblr and Wunderlist. I can add only from these widgets which would be displayed on my lock screen.

How can I add more app widgets to this list?
The only way to add more widget is to install an application that allow their widgets to be used on the lockscreen. Developers need to specify if their widgets can be used on the launcher, the lockscreen or both.

So, if a widget is available on the launcher but not on the lockscreen, I'm afraid that you can't use it on the lockscreen. (But you could mail the developer so he makes his widget available on the lockscreen).



As said in the comments, a Xposed module is available for rooted to user that enable all widgets on lock screen : GravityBox