Would it be hard to make us able to choose what patch we play on in custom games?

I would personally find it very interesting to play some things I couldnt get into because I only started about 2 years ago (e.g. old Xerath or old Karma). It would be fun trying different things out with friends or even in bot games. You're not forced to join a patch with a broken champ (/*cough Xin Zaho /*cough) since there is no matchmaking in customs. I could see however that there might be difficulties in implementing this. I'm not entirely sure, but I think the patch data is overwritten with every new update, isn't it? It would probably take a lot of disk space and time do this and of course, it is not a priority at all, but I would like to know if that is theoretically possible and what efforts would have to be made for it.