Info on uploading:
Publishing to the Web
More detail on Wordpress:
Instant Publishing from InDesign and in5 with WordPress Plugin
To make a Web App saveable, it has to be the only thing in the browser tab.
It cannot be inside of an iframe like it is inside of a WP post.
However, the WP plugin does have an option to open the content in a new window.
If you select this option and provide instructions to the user that they'll have to click that button before installation, it should work fine.