Multiple values in the DataValueField?

I have a dropdown box that is bound to a sql data source.  This is all done in my .aspx.  In my dropdown box, I display the employees names, and the datavalue has their TimeKeeperID.  THe problem I'm running into is trying to get the email address of the TKID selected.   I tried to list the datavalue field like this  "TKID, UserEmail" but it doesn't look like you can have more than one value in the datavaluefield of a dropdown box.  Isn't is possible to have more than one value in the datavaluefield of a dropdown box? 
 
<asp:DropDownList ID="ddReturnToID" runat="server" AppendDataBoundItems="True" DataSourceID="getEveryone" DataTextField="FullName" DataValueField="TKID"> <asp:ListItem Text="Please select One." Value="" /> </asp:DropDownList>
 
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