Hmmm, actually if you're locking two items to the two buttons you might be able to do this by another means.
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SUCCESSOR
is developing a script header to control inventory mechanics. One of his functions forces ZC to set a particular item to a particular button. If you were to run this script every time the Start button is pressed (so it would refresh when the subscreen is opened and closed) and just adjust WHICH item is forced based on which state Link is in (States 1 through 7, set variables ForcedB and ForcedA when switching to that state and then have SUCCESSOR's function equip those items) you could achieve what you're after. It wouldn't work if you want more than two items per state (since there are only two viable item buttons at the moment) but it might be easier than adding and removing the items from the inventory.