Originally Posted by deepinside
Can answer this myself now: successfully done.
I first tried to solder on the Mini-B plug of an USB cable I didn't use anymore, which was kind of difficult for me to get good access to. I broke off pins while trying to remove the "adhesive" around them. I also struggled with the smallness of the plug.
This time I disassembled one of the car chargers because I knew the Mini-B plug is already modified. I then soldered the +5V and Ground cables on an old A plug which for me was far easier to do.
I've managed to mod a cable too. I had a few mini-usb to USB A cables I could afford to ruin. I've come across two styles of mini-usb plug - one has moulded plastic and some sort of rubbery filler that seems to be glued to the internals of the plug. This was near impossible to rip off to enable soldering. Other plugs are just a clam shell design and can be very easy opened by pusing a craft knife in to the side of the plug.
A note of soldering... 5v needs to be connected to pin x - which is the 4th pin on the mini-usb cable - but actually labeled pin-x if you are working from a wiring diagram.
I was using a regular sized soldering iron... it was going to be quite hit or miss, I ended up leaving a massive blob of solder on the pin (and those surrounding it. Luckily I had a solder pump and when I tried to remove it, it sucked off the perfect amount and miraculously I ended up with clear unbridged connections.