By setting the toys up in centres of related items it stops one aspect of the hoarding in that if you want to play with the purse then you must stay in the doll area - stuff whatever food, dishes, doll clothes you want in the purse but that is all that is available for stuffing. If you want to play with cars and blocks then you stay in that area to do it.

I started that rule for a similar reason in that I had kids being bullies by taking a toy they knew another child liked to play with and then using it - while imaginatively like the blocks or cars were veggies in soup - but it wasn't about making soup and more about hogging the blocks and cars so others couldn't use them. I also hated the clean up because never made it back to where it belonged and the playroom was just a mish mash of bins stuffed with whatever was closest when I said clean up time. Limiting the mobility of different kinds of toys helped a lot.

Along with the sharing issue is also the issue of hovering. You may not stand there in the space of the child with a toy waiting for them to take their hand off it. Only after the child has left the toy in it's place and walked off can you move in and have a turn. Yes you may ask if you can join the child in play but if the child says no then you have to move on to something else and leave them to play. Again though it is ok to limit the number and breadth of toy any one child can hoard for solitary play.

When I have had a group of all older kids that were into sharing issues we used to play, then clean up and have a group activity then play, clean, group, etc. making 3 rotations per morning. When group was over I would draw names - in theory although I was really drawing the order I wanted so everyone got a fair chance to be first. When your name was picked you got up and moved to where you wanted to play. It allowed each child a fair chance to choose the favourite toy and also taught the others to deal with disappointment - cleaning up before though is key because it has to be put away rather than allowing another child to just take over someone else's construction or set up.