How to solder something very small

Where the brake hanger wires emerge from the chassis on the 01 diesel, there is a little plate. In 4mm scale it's about 2mm square (OK, triangular). This has to be fitted or the chassis won't appease the finescale gods. Doing this initially appeared tricky.

The problem is that solders goes where you don't want it and in this case, that meant the front face of the plate all over those lurvely rivets.

But, after a good strong cup of tea, the solution to the problem occurred to me. What I did was fit the wire through the chassis. Flux it both inside and outside the frames. Slide the plate over up to the frame and then solder inside the chassis.

Result: The solder flowed through the hole in the chassis and spread around the inside back of the plate. Just enough made it, something I suspect is controlled by capillary action or other science, to fix the item without covering it. This worked so well I did the other three plates like this, all look fine and needed no cleaning up. Excellent.