• Hire a batch of temps as "temp to hire" with the supposed idea being that you'll be offered a permanent position at the end of the temp period with satisfactory performance

• Set performance standards that are borderline physically impossible to meet

• After the end of the temp period, be like "Sorry guys, can't hire you on because you didn't meet our performance standards"

• Hire a new batch of temps

A plastics company I temped for did this at their injection molding plant; the whole complex was run with basically a skeleton crew of company workers/admin with a constantly rotating batch of temps making up the bulk of the workforce.