Well, I'm sure this is now illegal, immoral, and fattening (in the US at least), but when I was a cheap- *** summer painter I'd soak them for a day in a bucket, squeegee off what I could, soak them in another bucket with clean water, squeegee again, and then leave them in the tub while I took a long shower, squeegee, rinse, squeegee, etc. etc.
It's a pain in the ***, and I never could manage to get all the paint out. The covers would be fine for primer but too rough/ matted/ crusty for a good finish for interior work.
Any more, I just let them dry and throw them out.
ETA - If you're using the same color later, wrap the roller cover tightly in plastic and put it in the back of the fridge, it'll keep a while. Whether your lady will tolerate it, well...