You can download it selectively from https://www.posersoftware.com/downloads/content (with your serial number). Then install in a new runtime. Not using it? Delete the runtime. Easy.

I do find it annoying that every version of Poser wants to install all the old content in a new runtime. I already have multiple versions of that, please stop. Not sure whether Poser 12 has an option to just install all the new stuff.