Hand positioning for 2d items in Blockbench

Haiii! I have been using Blockbench for 3d modeling, and it's really fun! It's especially useful to be able to change how items display in the player's hands. I am going to be making large 2d item models for magic staffs, and I cannot figure out how to display 2d items on Blockbench or adjust their size and positioning. Any help? ^^