I have been working on a similar requirement however wasn't able to get this going but i did find a way to achieve the same functionality.
You can use nested SELECT queries to retrieve the initial attribute and pass it back to the second select query.
eg
SELECT tag_value as owner FROM tips_endpoints_attr_view
WHERE tag_name = 'Owner' AND mac_address = (select mac_address from tips_endpoints_attr_view WHERE tag_name = 'UDID' and tag_value = '%{Authentication:Username}')