Yay! ShardShare!
'Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life.'
T. Pratchett, 1948-2015 RIP, you are missed
E.g. A team of 4 gets a bandos chestplate. The chestplate is split into 25 for each player (100 total).
These shards can be sold on the GE or kept. Once any player buys/receives 100 shards of the chestplate, they can convert it into said chestplate.
This seems like a very simple but effective solution. It eliminates the issues with not having a sharing system (whereby a player can scam the rest of his team by not sharing).
It also doesn't create more coins in the game nor does it require the item to be immediately sold on the GE (i.e. forced sale).