Help with 'Alternative Colour Space'

[production temp]

Hello,
I'm working on some old files that we're putting on to print on demand with a leading digital printers.
I've come across a PDF book cover that has spot colours in the colour space but CMYK in the alternative colour space and my printers won't proceed with it.
Is it possible for a printer to use the alternative colour space?
I'm sure I can change the spot colours but I'd rather not have to resupply files to the printers as they will charge me!

advice would be much apreciated!

thanks
Amy