Budget Control - trouble

Friends,

Scenario is like this:

Client is upgrading from 4.6C to ECC 6.0. They are creating PR through Network and therefore the GR happens with Network as Account assignment. But the budget control is done with respect to WBS element. They have activated Budget Availability Control in ECC 6.0 using a package. Now they want to control the PO with respect to WBS element. How can they do that?

Please help.

Thanks,

A