If you want to short unused RCA inputs then what I've done is to take the cheap disposable interconnects that come with most components, chop them in half and then short the conductors (with solder) and put some shrink tube on the exposed end. Presto: two sets of shorting plugs from each interconnect that would otherwise be disconnected.
It's not hard to solder them because you are actually TRYING to short them. It would be much trickier to solder the conductors without accidentally shorting them !
It's not hard to solder them because you are actually TRYING to short them. It would be much trickier to solder the conductors without accidentally shorting them !