Hey,
there is no way to add Instagram, because they simply just do not support any interaction outside of their mobile app.
Quote from the original Instagram API:
At this time, uploading via the API is not possible. We made a conscious choice not to add this for the following reasons:
Instagram is about your life on the go – we hope to encourage photos from within the app.
We want to fight spam & low quality photos. Once we allow uploading from other sources, it’s harder to control what comes into the Instagram ecosystem.
All this being said, we’re working on ways to ensure users have a consistent and high-quality experience on our platform.
Therefore it is very unlikely that they are ever going to add a way for posting pictures without using their mobile app.
JP