If ours was a girl we would have got a second one, they are quite social little things. But being a male getting another male isn't an option as we have found 2 boys fight and it can be vicious! I haven't heard of them being trained, our male kinda poo's everywhere! But that could be a boy thing??
The trick to boys is finding the match. If you get a second male, he needs to be younger & introduced slowly. Bath both boys & all bedding/cage to remove any smells & then introduce the 2 over some yummy distracting food. Then watch. But always a much younger Male to an adult male.

They can be "trained"to use the litter tray also but I also found my boys to just poo everywhere. I haven't bothered setting it up for the girls & just vacuum the cage each day (inside on a fleece bedding.)