Special procurement key - STO from Multiple Plant at one time.

Hi

I have a requirement where one material A can be procured from several plants say 1000, 1100, 1200, 1300 at a time. We need to USE STO for this, but problem is that SPK can have only one plant at one time.

Clinet requirement is that he can ask for STO from any of these plants at any time. Even generating multiple STPReq, one for each procurement plant, at a time. How to map this scenario. There is no Quota arrangement for these materials.