Make a dummy upgrade with many many levels, it should apply armor bonus (If theres one that does a specific amount in the upgrade use it, else change the field 'Armor upgrade bonus' under combat on any unit able to use it).
When you acquire the item, it should either automatically perish else remove it with a trigger, then set the upgrade level of your upgrade bonus to either (Level of <ArmorUpgrade> + 1) or Increase level of <Upgrade> (WEU only?)