Customizing the PowerStore in this way is not a simple task. It would require a bit of editing and customizing to achieve this result and is not something that I would recommend for an inexperienced user.
The changes that are needed would require you to change the db, add in some more server behaviors to the admin pages, and then alter any page on the site that has to do with the items.
The tools that you would need to make the changes would be Digital File Pro and DataAssist. The edits that would need to be made to the front end would require you to edit the recordsets manually since they are too complex for DW to interpret. The same goes for the recordsets on the back end.
If this is something that you feel you are up to I can list some pointers but it is not a supported feature or something that can be easily implemented.