Tool Tip - Report Header dynamically picked and matched with a db value_

Hi Experts 

We are trying to enhance our reports by addition of Tool Tip .

For this we have created a Reference table in SQL db with 3 columns - Reportname , ReportColumn and Description and created a different dataset named - Tooltip.rsd with the query - which will limit my dataset to only the report which is running -

Select ReportColumn,Description from Referncetable where ReportName = @ReportName

Next we are using a Lookup function shown below - If the report column Header name is - Product Number - and this works fine .

=Lookup ("Product Number" ,Fields!ReportColumn.Value,Fields!Description.Value, "ToolTip")

Now - If I need to pick the column header value dynamically - I have used - =Reportitems(Mid(Me.ToString,20,InStr(Me.ToString,"_TextBoxExprHost")-20)).value - Which also works fine - But when I have used this function in Lookup - This does not works !!

=Lookup(Reportitems(Mid(Me.ToString,20,InStr(Me.ToString,"_TextBoxExprHost")-20)).value,Fields!ReportColumn.Value,Fields!Description.Value, "ToolTip")

Please help me using this function which would automate my work for tooltip 

Thanks in Advance 

--Saurabh

Thanks Saurabh Sharma