a/b testing and prototyping

I've been trying to find a plugin or other method to perform two distinct functions for my large WPMU+BP site:
* prototype testing
* A/B testing

I've found this plugin (A/B Theme Testing Plugin - by Aaron), which asserts support for A/B testing, though it appears to be exclusively pushing A/B testing, and not the ability to leave one theme in place (current) while allowing the developer to test (prototype) a new layout, INCLUDING widgets.

I also found this plugin (SES Theme Split Test), which does allow you to force a specific theme for yourself, but doesn't appear to work at all in my environment, and even if it did, it doesn't support widgets for the alternate theme(s).

Initially, what I need to be able to do is test and tweak a new theme on a very active site, without disturbing the current home page (prototyping). Once it's fully tested, I hope to activate it as simply as possible, preferably without having to then migrate a bunch of widget settings from another blog.

Then I require the ability to perform A/B testing between multiple themes, again, with unique settings for each of them.

Ideally, this would allow me to preview the site, edit widgets under both/multiple designs, without having to migrate any settings (such as widgets) when switching/activating themes or during and after testing.

Keep in mind that this is a very active WPMU+BP site, so the downtime between simply activating the new theme and adding all the necessary widgets to the layout (say, if I were to use a secondary blog for testing), could be very tacky-looking to our users, and would be best avoided if possible.

Is anyone aware of a plugin or other system that'll do what I'm after? I've been told NOT to simply activate the theme for a secondary blog, because it can negatively affect the BP installation. And even if I go this route, it would require me to manually migrate settings once I was satisfied with the changes.