There are 3 ways to do this
1) make it a loop as well as a one shot, then it will loop until you press it again – it basically lets you toggle the sound on and off.
2) add it to a choke group with another sample that is silent (you can do this by taking any sample and turning the volume down to zero). The silent pad will stop the long sample when pressed.
3) if you don’t mind stopping the playback of koala’s sequencer, just double-tap the play button.