Combining Prefill with Progressive Profiling would be an option.
If not, keeping prefill and using a simple JavaScript to blank the relevant fileds would be a good alternative.
It is necessary to view the page source, tke the ID of each field to blank and add to the script.
In the example bellow the word script was replaced with s-c-r-i-p-t to avoid the portal interpreting as instructions
<s-c-r-i-p-t language="Javascript" src="/js/public/jquery-latest.min.js" type="text/javascript"></s-c-r-i-p-t>
<s-c-r-i-p-t type="text/javascript">
// use no conflict mode for jQuery
var $jQ = jQuery.noConflict();
// when the page is ready, change FirstName and newValue
$jQ(document).ready(function() {
$jQ('#FirstName').attr('value','');
});
</s-c-r-i-p-t>