... how do I shorten the input jacks?
Make a simple RCA shorting plug by taking a short, cheap RCA interconnect. (The cheap ones that come with most audio/video devices) and simply cut off one plug leaving about 1/2" wire. Remove the insulation from the wires. Twist/crimp the ground wire to signal wire and you have your shorting plug. Need two, cut off another!! Save the interconnect to make two more when you lose the first plugs!
You can get fancier, if you want. Solder a 220-1K resistor between the ground and the signal, but really not necessary in this application.
I usually put a bit of shrink wrap on the exposed wires, on the cheap method, just for that final beauty touch!
Cheers,
Geary