PO TAB rule based on DFF as source

For expense requisitions, we use requester's default expense account to derive the cost center segment of the charge account. For some purchases (requisitions) such as Laptops that IT helpdesk creates on behalf of the users, they don't use the user as the requester, instead they use IT helpdesk agent as the requester to drive the approvals and receipt confirmations etc., but those requisitions should use the user's cost center from default expense account. We created a DFF to capture the user (original requester). Is there a way to use DFF as the source and use the expense account of the