Jason, thanks for your comment on the previous post. What particularly resonated with me was "Making it work for real would be a big deal where I work," because I'm part of Premier Support for Developers and our job is helping enterprise and ISV Microsoft customers with their app development issues. Customers buy an annual contract (there is a range of sizes) with my team and we work with them through the year so we get to know their systems.
I've just posted two articles under the Software category on the subject of SxS Managed COM - i.e. a native app activating an unregistered COM-Callable Wrapper which then delegates on to a managed class library. Generally the CCW would have to be registered but the SxS mechanism uses .manifest files to build in-memory structures known as Activation Contexts.
The two articles mention associated .zip files. I haven't included a link to these but there are clear steps in the articles (with source code and explanations) on how to produce the binaries for yourself. I hope these are of some use. Please note that the 'With Manifest File' article applies to Windows 2003 only and the 'With Manifest Resource' applies to both Windows 2003 and XP, so please choose the approach which fits your platform requirements.