Hi,
As mentioned there are two option for your requirement.
Option 1: You can do the necessary settings for the document stored in GOS to routed through content server other than application server which will load your system.
Option 2: You can create a object link for Invoice( PO is already exist) and attach the document from the transaction (MIRO) using the object link settings as 2.Please find the screen shot for your reference.
Rgds.
Nayeem.
