Can't you replace them with the stand-ins?

2016年12月四级真题（第二套）听力 Section B

Get on the phone to Tom, and try to get their stand-ins over tonight.

2016年12月四级真题（第二套）听力 Section B

I'm afraid not, the stand-ins are already in use on line 6, and the ones from line 6 are being serviced.

2016年12月四级真题（第二套）听力 Section B