If so, might I suggest inboxsdk.com for help with your extension dealing with Gmail.
You're right -- since these apps don't (yet) embed our SDK in to their site, we need to get the current state (eg current page, selected table, etc) from the Chrome Extension. But our goal is to provide entire entire extensibility platform in an embeddable JS snippet, so hopefully that won't be the case long.
Other than our InboxSDK, you could also look into building a gmail addon and having your users install that, but it would be another install in addition to your chrome extension.