How to store json data in session which returns from background method?

Based on user request in zenpage, i am running the method ConvertMDXtoJSON in background and loading the status in progressbar.

D ..%RunBackgroundMethod("ConvertMDXtoJSON",MDX)

From this background method ConvertMDXtoJSON() i want to return the value(sjson) and store it into session.

How can i do this?

Below is my code. 

ClassMethod ConvertMDXtoJSON(pMDX) As %String
{
  Try 
  {
      Do ..%SetBackgroundMethodStatus("Started",0)
      set Params = ""
      set pStatus = $$$OK
      set RS = ##class(MS.Deepsee.MDX2JSON.ResultSet).%New()    
      set pStatus = RS.%PrepareMDX(pMDX)
      return:$$$ISERR(pStatus) RS
      set pStatus = RS.%ExecuteAsynch(.QueryKey,.Params,0)
      s pCubeName="StockDetail"

      // Gets progress Percentage
      set prog= ##class(%DeepSee.ResultSet).%GetQueryStatus(pCubeName, QueryKey,.tComplete,.tSC,.tPending)
      while (prog<100 )
      {
            set prog= ##class(%DeepSee.ResultSet).%GetQueryStatus(pCubeName, QueryKey,.tComplete,.tSC,.tPending)
            Do ..%SetBackgroundMethodStatus("Percentage completed",tComplete)
      }
  }
  Catch {}

   set obj = RS.ToProxyObject(.st)
   return:$$$ISERR(st) st
    //$$$DynObjToJSON(obj)
   Set tInitIO = $IO

    // we MUST use %ISCJSONStream variable used by mnemonic space ^%ZEN.Auxiliary.jsonProvider.1 as output redirection container
    set %ISCJSONStream=##class(%Stream.TmpCharacter).%New()
    use tInitIO::("^%ZEN.Auxiliary.jsonProvider.1") // this routine – here as mnemonic space – is created during %ZEN.Auxiliary.jsonProvider class compilation
    do ##class(%Library.Device).ReDirectIO(1)
    $$$THROWONERROR(tSC,##class(%ZEN.Auxiliary.jsonProvider).%ObjectToJSON(obj))
    If ##class(%Library.Device).ReDirectIO(0) Use tInitIO
    do %ISCJSONStream.Rewind() 
    set sjson = %ISCJSONStream.Read() 
    Do ..%EndBackgroundMethod()
    Q sjson
}

ClassMethod %OnMonitorBackgroundTask(pTaskID As %String, pStatus As %String, pPercentComplete As %Float)
{

Set pMsg = pStatus _ ": " _ +pPercentComplete _ "%"    
if pPercentComplete>0
{
&js<
document.getElementById("Percentage").innerHTML='#(pMsg)#';
document.getElementById("prog").value='#(pPercentComplete)#';    
>
}
}

ClassMethod %OnFinishBackgroundTask(pTaskID As %String)
{
#; Clear HTML component    
&js<
document.getElementById("prog").value='100';
document.getElementById("Percentage").innerHTML='Finished';
document.getElementById('sframe').src="../msdeepsee/MS.Deepsee.Frame.cls"
>
}

After finishing the backgroundtask, loading a iframe. there i need to get the status(sjon).

Give me some suggestion.