A new type of 'trade' option can be added when targeting a crafter, call it 'request craft' or something. The window will be similar to the synthesis main window, but without the recipes or requested items button. also the person requested to craft wont be able to add items to it.
-The requester requests craft, the crafter accepts.
-The crafter does the kneeling bit. the requester then adds the materials into the window.
-after they are all added, the crafter selects main hand or off hand and begins crafting.
-after completion, the item goes directly to the requesters inventory.
This way, there would be no need to trade items directly to the crafter. also, more items could be made untradable this way. It would also be a good method for the new materia system (Name Tentative)