You can pass a setting to prevent the shipping address from changing.
You just have to add this with the other parameters being passed:
$nextIndex = count($WA_PP_ECO_Set_params);
$WA_PP_ECO_Set_params[$nextIndex] = "addressoverride";
$WA_PP_ECO_Set_params[$nextIndex] = "1";
If you can't spot where to add it, just attach your confirm.php page and I can give you a line number. You can add it right after the address or phone number.
That will prevent them from updating the address once passed to paypal.