The Casio keyboard is only capable of half pedaling with the proprietary 3 pedal unit.
Do you know this for sure - have you tried plugging a pedal like the Roland DP-10 into the 1/4" plug? I'm not planning to use it with a computer so a midi box is not useful for me.
Yes, I have. That jack has two contacts, suitable for a simple "on/off" sustain pedal like the M-Audio SP-2 (which works very well).
If the PX-160 is the same as the PX-150 (my bet), Beakybird has nailed the possibilities. Except for one:
. . . Take a Casio triple-pedal unit, and cut off (unscrew?)
. . . the plastic mounting bar.
That would give you a "travel-size" triple-pedal unit, compatible with the PX-160. You could solve "slip-and-slide" problems with a bit of ingenuity.
When you say "I'm planning to use it with a computer" --
. . . What does that mean?
If you're going to be using "virtual piano" software, that supports half-pedalling, Beakybird's MIDI suggestion is a good one.