Mods like Productive Bees and Resourceful Bees have their bees isometrically rendered in the jei sidebar as if they were items. Being that it seems possible that you can pull entity models to show them in the mob drop menus, I couldnt see why they could also be rendered in the sidebar (likely unanimated. as the bees mods bees are animated and cause a considerable performance decrease when scrolling past them). Allowing players to search for mobs, and by extension their drops, spawn locations, rarities, etc. would be really cool.

That would be cool, but I would have no clue how to do that

I think they use an item for this and attach a TileEntityRenderer to it.
With a TileEntityRenderer you can render you item as you like.
That's just a guess but that's how I would approach it.