Hi Daniel,
You can definitely achieve this via customizing using Excel VBA. You can put a button in PO report which populates a custom list box in the PO report where by the user can select Cost centers(Populate all cost centers in PO report) for which he would like to plan.
Once he selects a cost center, pass that value to a cell in Input Schedule where Forecast planning for particular cost center needs to be done.
There In Cost Center Olap Member formula just refer the cell where u have passed the value via list box.
You can also put code in list box where by once he clicks on OK button in, report 2 automatically refreshes.
Let me know if you need any help.
Regards,
Raman.