Is it possible to use a flexfield attribute from the requisition header in Manage Account Rules?

We are using Procurement Transaction Account Rules to derive the cost center from the Charge Account in the purchase requisition.
We need to create a rule that uses a flexfield from the purchase requisition header as a source. But we do not find this option available in Manage Sources.
Is it possible to use a flexfield attribute from the requisition header in Manage Account Rules?