UPDATE- WORKING CODE BELOW
The key was creating a custom data attribute as @Fil indicated in this link (http://html5doctor.com/html5-custom-data-attributes/) and passing from the code behind and then accessing the $.cache. And passing the clientID of the reportviewer into the javascript function to get to the current instance of the webpart child controls.
<input type="hidden" id="<%= ASP_SSRS.ClientID %>_myDataState"
onchange="compareUnitValues(this.id, this.parentNode.id, '<%= ReportViewer1.ClientID %>', '<%= ASP_SSRS.ClientID %>', '<%= btnSendHiddenField.ClientID %>');" />
<script type ="text/javascript">
function compareUnitValues(elemt, parent, reportviewerID, value1, value2) {
var myDataUnit = $("#" + elemt),
parentObject = $("#" + parent),
reportviewerObject = $("#" + reportviewerID),
ssrs = $("#" + value1),
btnSend = $("#" + value2);
var myDataUnitValue = myDataUnit.val();
var myDataUnitJSON = jQuery.parseJSON(myDataUnitValue);
var currentmyDataUnit = myDataUnitJSON.currentUnit.objectId;
var sessioncurrentObjectId = document.getElementById('<%= hiddenCurrentObjectId.ClientID %>').value;
ssrs.val(myDataUnitValue);
var currentReportViewerParam = $("#" + reportviewerID).attr("data-report-param");
if (currentmyDataUnit != currentReportViewerParam) {
btnSend.trigger("click");
}
}
FROM CODE BEHIND CREATE THE CUSTOM DATA ATTRIBUTEReportViewer1.Attributes.Add("data-report-param", parsedObjectId)