We had a baby gate on Darcy's room. Even if it's not 'his room' can you make him a special place that's safe to play with his little toys like that? I also had one on my craft room so if she wanted to do craft then it had to be in there.
She was pretty good about only bringing stuff out if he was asleep. for a while we did have a safety gate across the hallway so the bedrooms/bathroom/laundry were off limits and that worked pretty well.