Sears sells 1/4" - 3/8" - 1/2" pipe-type inserts that come in a small red plastic pouch. Usually locked up in the cases with their other hand tools. There's very little protrusion from these. You slip the appropriate extension into your 14mm, then use a long open-end wrench on the extension.
These gadgets are designed for working in tight places. Don't remember the Sears part number.
When I do my 126 differential fluid, I first back the car up on ramps in order to secure enough clearance to slide a piece of pipe over the end of the open-end wrench.