I was able to use javascript to get the form values and then dynamically create the url with the form values. A bit hacky but it worked. Let me know if anybody has any more elegant solutions.
<s:a id="exportLink" href="%{excelurl}" onclick="document.getElementById ('exportLink').href=(document.getElementById('exportLink').href + 'startDate=' + document.getElementById('startDate').value + '&endDate=' + document.getElementById('endDate').value ;alert(document.getElementById('exportLink').href);">Export Current View to Excel</s:a>