I was trying to set up a item macro as well. I don't think it is possible yet... I am not sure why, but hopefully they will add it back in.

Is there a reason you are wanting to use an item macro instead of setting the item to your hot bar?
I don't know about the OP, but for me, I wanted a Second Wind + Hi-pot macro.
/ac "Second Wind" <me>
/item "Hi-Potion" <me>

This would use second wind if it was not on cool down, if it was on cool down, it would use the Hi-Pot. I want as few things on my hot bars as possible.