When you say that you can't install anything by 2014.04.14, what do you mean?

You can obtain the latest version here: https://github.com/koreader/koreader/releases

Since you have an older version installed:
Start your Aura in nickle, connect it to your computer.
Remove the old koreader folder from the .kobo folder.
Copy the new koreader folder into the .kobo folder.

Now you should be able to restart your Aura in KSM and launch koreader.

This process should be fairly safe since it doesn't affect KSM or nickle, but there is always a greater risk with unsupported modifications.

If it is producing error messages or koreader doesn't start, please let us know what's happening and perhaps we can give more meaningful help.