separations on A2 sheets from either indesign or acrobat

Before printing to a risograph i need to manually separate colors. Easy peasy you'd think, but no. I'm using mac (and the students I'm teaching mostly uses mac) and Riso have no driver to their A2printer for mac.

So ok, let's use Acrobat, and create a pdf, but mac does not allow pdf-printers to be installed so I cant use the easy to use separation-function in the advanced mode of Acrobat print. 

So ok, let's use Indesign print to file (making a ps file that i can distill to pdf). Sweet. No probs. Other than that I'm limited to the page sizes of whatever printer I have installed, none of which have A2 as an option and custom won't allow me to exceed said printers page size limit even tho I'm not ACTUALLY printing on it, just producing a file. And I cant have the riso driver. And i can't have the pdf-printer driver. I'm stuck.

What I want: CMYK (+ spot-color) separated pages on A2 paper produced from either Indesign directly or via a pdf in Acrobat, all done on a Mac. Can anyone help, is there a workaround that I don't see?