Did you ever find an app for adding shipping Insurance like you were looking for? You should try Guide Shipping Protection, its 100% free for merchants. Plus when we have to replace a package that is lost/damaged/stolen you will receive the extra sale/revenue from our replacement order.
You can find it in the App store homepage under New and Noteworthy, or you can follow this link and check it out for yourself. We would love to work with you and hope to hear back!