Hi Fatcat, dividing the screen is remarkably easy with Mogami 2549 for making a DIN to RCA cable. Most RCA paired sockets are close together, typically 1 or 1.5 inch or so (I note you used "foot" measurement) & about double that is all thats needed for the "Y" divide, or longer if you prefer.
The screen is a spiral wound wire covering & is easily "split" into two - see pictures
I made a DIN to RCA for a friend - at the RCA end I stripped back about 4 inches, divided the screen in two, & put each channel + & - pair into a section of insulation tubing. At the RCA dividing point I fitted a short section of heat shrink to bind the separation point together. Soldered on the RCA plugs & its done. Sorry I didn't photo it (unusual for me) but it looked like a 5 ft long DIN cable with a little "Y" section at the other end with RCA's fitted.