Is there a way to automate upload of extension.zip to a jive instance?

It's absolutely possible.  If you can do it in the browser, you can write an app to do it.  You just need to mimic the HTTP calls.  I would start by using the JS console in the browser to capture the network traffic for when you upload the extension.zip and then wok on mimicking it.

Many many years ago when I worked primary in Perl I used a module called WWW::Mechanize for this (WWW::Mechanize - search.cpan.org).  For Java you might want to use something like Selenium's web driver (Selenium - Web Browser Automation) or HTMLUnit (HtmlUnit -        Welcome to HtmlUnit).  But there are a lot of other tools out there for this.  These tools are primarily meant to be used as testing tools, but there is no reason why you couldn't use them to automate it.

Some more modern tools may even be able to execute the JS code in the page, although typically you won't need this.

It isn't straight forward, but it is possible.

We’ve talked about this internally, and I’ll need to confirm.  I do not remember if this was available, but had some major limitations and/or it was a hack-day project that hasn’t been pursued further.

Stay tuned.

Edit:  To clarify my answer, it is about an official service purposefully designed for this use-case. Robert is correct, but you will need to handle the CSRF protection which would get tricky, but again...nothing is technically impossible when it comes to stateless traffic synthesis. =)

All, As we move forward with the platform we see this requirement becoming essential, especially with some planned upcoming features.  Right now, we do not have any reliable means to deliver on this requirement, better than that suggested above.  That being said, the platform is headed in a direction where this feature will become very relevant, so I can assure you it is being discussed (apparently even prior to this conversation).  So stay tuned to the Developer Blog & Developer Webinars, as I'm sure we'll announce it first there, but note that timing is still up in the air at the moment.

Hope that helps, with as little concrete information that's in there. =\