What meta tags have you tried?
<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">
<META HTTP-EQUIV="PRAGMA" CONTENT="NO-CACHE">
should tell Safari not to cache, but I have not tried them.
You could use javascript to load your "real" startup page from the cached page using any of the standard techniques to make the URL unique, such as adding a random number.
That might even work for the main startup page, but I doubt it. Worth a try, though.
I suggest the cached page load a new page only if it is on the springboard:
UNTESTED suggestion:
window.onload = function () {
if (navigator.standalone) {
document.location.href = 'http://your.com/whatever.php?randomjunk=1234') }
}
so if the page is in the browser it can give instructions on saving to the home screen and if it is run from the home screen it will load the real page.