One thing I've been thinking. You might be able to find someone to convert a pair of straights to circulars. Cut off the ends opposite the tips, then use a drill press to drill a very small hole down the center length on the cut ends. Then glue a cable in between the ends and sand the ends to taper down to the cable.
After I make my move to California, I will have full access to a shop. With the wizardly skills of DH, FIL and BIL, and of course... ME!!! :roflhard: I could make one for you.
I measured my Addi interchangeables today, size seven, and the length of the needle is the same as the length of the Flex needle, so I don't know if the Flex needles will work for you.