- Type a name whatever you want on 'Add a new search engine' field.
- Add 'Keyword'. (NOTE: The keyword will to be your customer shortcut, choose wise. :D)
- Then open 'Bookmark Manager'. Copy 'Read it later' URL to 'URL with %s in place of query' field.
- Delete 'Read it later'.
Just type your customer shortcut on Ominbox, then the page you current stay will be saved to Instapaper. You can also add customer shortcut to your most visited page. :D