Ok, so as no one responded to me on this 
, I can report back to the equally disinterested that I ultimately decided to go with the Dension BT Lite unit, having acquired a CD43 to replace my existing cassette (which cost me an arm and a leg because of the Mini branding, but that's another story).
This isn't a product endorsement or anything and I am not associated with the company in any way. I thought I might just post this in case someone might be thinking of doing this themselves and looking for the right product for the job.
So, this little box essentially gives the CD43 bluetooth connectivity by mimicking the presence of a CD auto changer. Although the Mini never had this option, the head unit itself is still geared up for it, as they put the same radios in the BMWs of the period, which did.
Having dragged the whole dashboard out, I decided the best place for the box was behind the glovebox, as this would still allow me to connect up to the included USB port for firmware updates, without having to remove the radio itself. This was attached to the bulkhead with the aid of a couple of strips of velcro. A tight fit, but just enough wiggle room left between the back of the glovebox and the unit.
In addition to playing music via Bluetooth, I was also after a neat way of charging my phone on the go. As mine is a later car, it does not have a cigarette lighter, so I was pretty stumped every time I used the sat nav on my phone to go anywhere, as it would struggle to last the whole journey if it was a long one. Thankfully, as well as Bluetooth support, the Dension unit also offers an additional option for a connecting up your phone cable to a neat box housing a female USB. Again, looking for an inconspicuous place for this, which would still be accessible without a load of trailing wires when not in use, I chose to mount this to the lower dash rail on the passenger side. This was held in place by another a strip of velcro. When sat down, the rail itself hides the box from view, so you would only see if it you knew it was there.
A final feature which I took advantage of was the handsfree. The box comes with a microphone, which I routed through to the driver's side and clipped onto the lower dash rail again. This is necessarily the best place for call quality, but again I didn't really want it to be seen and dragging out linings etc just wasn't going to be acceptable. The good thing is that when a call comes in, the call can be answered on the radio itself and whatever is playing is paused for the duration of the call. The whole conversation is then audible over the car's speakers.
While I was fitting the dashboard back in, I also took the opportunity to re-engineer the centre most bolt to act as a support for the radio. I had some initial problems with the head unit popping out due to the slightly different way the radio clings onto the dash. Rather than sit in a cage as my cassette unit did, the radio secures itself with two little wings at either side, which tighten up against a very shallow lip in the dashboard's radio aperture. It's not the most secure of fits at the best of times, let alone with the extra strain of supporting the radio's weight too. A longer M6 bolt with a couple of extra nuts and washers to act as a shim did the trick. A tiny bit of velcro on the underside of the radio would then stop any rattles from potential metal to metal contact (or earthing issues, hopefully!). Seems to be holding up well so far.
I have taken a few snaps while I was down there tonight to try and illustrate what I have described, though they are a little dark as the light was going.
Hopefully someone will find this useful. I think this is a great little product; just what I needed. Although there is no support for showing the track name on the stereo (which I see as the only real downside, but is presumably a limitation imposed by the head unit), you do have basic back and forward control for tracks, so you can skip along direct from the radio controls.
Jacob
Edited by Tumbleweed-Connection, 29 July 2015 - 11:38 PM.
