I know what you mean, but haven't managed to find out whether the three wires are available as pins on the 21-pin version of the decoder, in which case you're wiring onto a circuit board rather than the chip.
To be honest it's not that tricky - the decoder will likely be clean, you just need a small soldering iron bit.
What, you mean you haven't got one specifically for electronic jobs . Quickly tin the wire end and trim them so that there's only a mm or two of shiny stuff exposed at the end of the insulation. They should still have a little blob of flux-rich solder on the end of the wire now. Place wire on decoder, apply iron and wait for the solder to 'flash'. Remove iron. Done.
Steph