Take a look at the Data Analytics module. It allows for custom field creation.
Consider using custom data forms. You can have a form that is sat on the PC and manually completed when the device is assigned. Data will be returned with the inventory information. It does mean adding that information on the PC itself though.
Will these machines still be reporting in via a cloud appliance/management gateway?
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Update - WoW & State Notifier now integrate for even more functionality
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