[Imajie]

Assuming you're using EasyC you want to add something like this to your Operator_Control function

if(GetOIDInput([joystick port], [button]) == 1){
    //Button pressed so drive motor
    SetPWM([port], [value]);
}
else{
    //Button not pressed stop motor
    SetPWM([port], 127);
}

I believe that 3 and 4 are the numbers for the aux1 and 2 but I could be wrong.