I don't know where this basic idea comes from - but I got the tip of this combiner from SM0IQC. Since the use of regular 2 to 1 combiners requires some more effort, I thougt this 4 to 1 combiner would be a nice compromise. Why a compromise? Well, there are no free lunches!
By connecting everything together like the schematic below, the isolation between the different PA's is not near what it would be with set of 2 to 1 combiners. However, with todays LDMOS transistors the chance of a damaged PA is far less than with e.g. bipolars. Hence, I decided I'm willing to accept this compromise.
The semi-rigid parts are all 50 ohm and effective quater wave. Check the specification for the velocity factor of the coax in question and multiply the free space quater wave by the velocity factor. I ended up with 41mm on 1296MHz and 123mm on 432MHz. I allowed some space for the soldering connection and I did cut my coaxes 40mm and 122mm with about 0,5mm of isolation and 1mm center lead.