Is there any way to talk her into keeping him with the litter for a couple more weeks?
I got mine at three weeks old, and they did ok. I tried greens with them, because I couldn't be sure they were eating enough pellets and they didn't eat much hay, but the greens always resulted in soft poo. By 4 weeks, I knew they were eating well enough on the pellets so I stopped worrying. They only get pellets, hay, and grass.
They're 7 weeks old today(ish) and about three lbs each (poppy was 10 oz and hazel was 12 oz when I got them), so I think we did ok.
Good luck with your little (big) guy, and don't forget those pictures!