I think I'd try: 

If you have a spare tank available already containing adequate nitrogen -- transfer all the straws out of the canisters into the other tank.   Keep that spare tank handy.

Then take the 6 empty cansiters out of the tank and pour the nitrogen into a styrofoam cooler and hopefully the straw will land in the cooler as well.  Remember the straw might possibly get somewhat caught in the spider, in the bottom of the tank, so you might have to shake it some .  And don't take too long after the nitrogen is dumped, you're working on borrowed time.   

REMINDER: don't reach into the cooler to retrieve the straw, have some sort of applicable tweezers or such to grab it, transfer it to the spare tank with the rest of the straws.  If it took a little more time than you're comfortable with, either throw the straw away or keep it seperate so you can use it in a not so 'special' cow, just in case it is less than perfect. 

Have a funnel handy and pour the nitrogen back into your tank as soon as you've retrieved your straw.