Hi jpike,
This should be possible by changing the 'ColumnNumber' column of the 'CustomPollers' table directly in the database. Here's simple example of the SQL query which should help you to do that:
UPDATE CustomPollers
SET ColumnNumber = 10
WHERE UniqueName = 'Tx_Bytes'
Executing this will move the 'Tx_Bytes' poller to the position 10. By default UnDPs have the ColumnNumber set to 0.
Hope this helps,
Zbynek Botlo