you can't how pliable they are, but you can 'de curl' them.
1--drop needle in small bowl of hot (from the kettle) water,
remove after a few seconds, with a cloth, dry and pull straight.
2 use a hair dryer to warm plastic and pulll straight (usefull if you have stitches on needles!)
when i learned to knit, circ's often had metal cables.. (i still have some circ's with metal cables, see my blog (i posted about my collection needles a few weeks ago)
after learning on them, anything is easy!