Re-add Scrollbar Inside Popup Window?

Is there any way to re-establish a vertical scrollbar inside a popup window if the parent window opened the popup without scrolling? For some reason, the asinine people at the local mls decided that their virtual tour links only need to be 800x600 with no scrolling. Here is what I am using to resize the window onload - but I still cannot scroll the page down to see the rest of the page, if this page is not loaded full size:

Code:
var originalWidth = window.innerWidth
var originalHeight = window.innerHeight
function addLoadEvent(func) {
var oldonload = window.onload;
if (typeof window.onload != 'function') {
window.onload = func;
} else {
window.onload = function() {
if (oldonload) {
oldonload();
} func();
}}}
if(originalWidth < 1000){
addLoadEvent(function() {
window.innerWidth = 1000
})}
if(originalHeight < 500){
addLoadEvent(function() {
window.innerHeight = 500
})}
Is there something I can add to this to re-establish the scrollbar?