Identifying field in F4301|F4311 to store reference requisition no

Hi,

I have a small Q. We have recently implemented procurement at a client. At the moment, they are not using requisitions but they plan to after a couple of months. As an interim measure, however, they need some field to store that requisition no. The field should be such that it is available on various procurement inquiries and reports. At present they are using "Pmt Remark" field in PO header BUT they are not able to locate this field on any of the procurement reports and inquiries. Any suggestions in this matter will be much appreciated. Thank you.