If you want 6 or 10 pin and budget is no problem, maybe Tag-Connect? http://www.tag-connect.com/catalogThey are used for programming microcontrollers, so the plug/cable is expensive, but no socketis needed, just a specific pad/hole layout on the PCB.
Measured DuPont.10mm long, 5mm wide and 15mm height (in the direction of the cable)
This is dirty but - if the use is really infrequent, you can even use standard 0.1" header holes, and put header into those holes and apply gentle pressure at an angle with your hand to keep it in contact while you program it. This is how I bootload the boards I sell that don't come with pin header attached.
I want to be able to occasionally connect a cable with 8 wires to an AVR that is on a small PCB. It's the connector on the PCB that I want to be of minimum length, width and height. An FFC connector is one possibility but I'm sure there are many others.