After a lot of searching, I've found two vendors that come close to what I need, and I'm giving this answer to my own question in the hope that it will help others:
Grabba seems to be working on a sleeve design that connects directly to the device (HTC Desire HD 2). This eliminates the hassle of dealing with a bluetooth connection (in many production environments the user simply don't have the skill set to deal with that). Unfortunately it isn't released yet. The plus is that the HTC Desire HD 2 is an excellent device.
Sumlung have a bluetooth reader with a sleeve design. I'm not sure the design is stable enough with many devices. The plus is that it is available for sale right now.
If anybody finds a reader with sleeve design for a decent Gingerbread device, preferably with built-in high-capacity battery, I'll be more than happy to make it the proper answer to my question.