At first attempt, I can't even use search_literal because the string is stuffed into a WHERE clause:

$schema->resultset('foo')->search_literal('EXCEPT SELECT * FROM bar')
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becomes something like

SELECT * FROM foo WHERE ( EXCEPT SELECT * FROM BAR )
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What about:

$schema->resultset('foo')->search_literal( '1=1) EXCEPT (SELECT * FROM
+ bar' )
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Just _might_ fall into the category of "Hack" though :)