The commented out section is a "proper" way to do it.
It inserts a new textbox into which you would type your password, then a button to press that hashes the password using the Westpac-provided one time pad and inserts the result into the real password box.

It doesn't work for me and I gave it a shot at fixing it but could not.

Instead I rewrote the bit at the end to just insert the password that's in the source code. This does mean that your password is stored on disk.

// ==UserScript==<<BR>>
// @name          Westpac Logon<<BR>>
// @namespace     joelhockey.com<<BR>>
// @version       1.4<<BR>>
// @description   Fix the Westpac logon page to allow normal password entry<<BR>>
// @include       https://online.westpac.com.au/esis/Login/* <<BR>>
// @grant       none<<BR>>
// ==/UserScript==<<BR>>

// new submit function <<BR>>
// function newsubmit(event) { <<BR>>
    // var typedPwd = document.getElementById('pwdinput').value; <<BR>>
    // var pwdFix = ''; <<BR>>
	// for (i = 0; i < 6; i++) { <<BR>>
        // pwdFix += keypadDef['malgm'].charAt(keypadDef['keys'][typedPwd.charAt(i).toUpperCase()]); <<BR>>
// } <<BR>>
    // document.getElementById('password_temp').value=pwdFix; <<BR>>
	// // alert("hello"); <<BR>>
// } <<BR>>
 <<BR>>
// window.addEventListener('btn-submit', newsubmit, true); <<BR>>
 <<BR>>
// // put the pwd box on the screen after username <<BR>>
// var username_temp = document.getElementById('username_temp'); <<BR>>
// var pwd = document.createElement('div'); <<BR>>
// pwd.innerHTML = '<label>Password</label><input id="pwdinput" name="pwdinput" type="password" value=""/><button type="button" onclick="newsubmit()">DoIt</button>'; <<BR>>
// username_temp.parentNode.insertBefore(pwd, username_temp.nextSibling); <<BR>>

// put your username and password here if you want to <<BR>>
// IT IS A SECURITY RISK IF YOU DO!!! <<BR>>
document.getElementById('username_temp').value='44455666'; <<BR>>
var pwdfix = ''; <<BR>>
var typedPwd = 'hunter2'; <<BR>>
// console.log(keypadDef['keys']); <<BR>>
// console.log(keypadDef['malgm']); <<BR>>
for (i = 0; i < 6; i++) { <<BR>>
        pwdfix += keypadDef['malgm'].charAt(keypadDef['keys'][typedPwd.charAt(i).toUpperCase()]); <<BR>>
} <<BR>>
// console.log(pwdfix); <<BR>>
document.getElementById('password_temp').value=pwdfix;}}} <<BR>>