SAP NetWeaver 7.5 LAMP integration

Dear Everyone,

We have a PHP rich web application sitting on Apache and MySQL, and we would like to integrate SAP ERP 6.0 on NetWeaver 7.5. I saw that there is a possibility of using REST API (https://archive.sap.com/documents/docs/DOC-51570) but this requires development on our customer's side, and even their policy might not allow to open up thier NetWeaver. Other solution could be to import .csv, but that is not very user friendly, and doesn't let the two application achieve synergy. Is there any other ways I looked over to achieve cooperation between these two applications using very different technologies?

thank you in advance, Zsombor