External system calling SAP ECC enterprise service.

Hi Experts,

We have an external system(out of the client network) which needs to call the Enterprise service ExchangeRateByExchangeRateQueryResponse_In  in ECC.

As we  don't want to open the ECC port to the external systems we thought of using SAP PI in between.

I can develop a  SOAP to SOAP scenario between External system and ECC using PI.

I want to check whether there is any better  way of doing it without developing the interface.

Thanks in advance

Regards,

Rajesh.A