It's not as easy as I've expected
The S7-connection in TIA uses a TSAP connection ressource of 10 hex, which cannot be modified. This ressource means, that this is a configured connection and so it needs to be configured in the PLC as well, otherwise it will refuse any connection attempts with this TSAP.
If you use an unspecified connection, then it uses connection ressource 03 which has not to be configured in the PLC - but then you don't get the symbol connection.
If you've got PLC and PC-Station in the same project (TIA or Step7) it's an easy task, as you only download the PLC after configuring the connection and it runs. But if I understand you correctly, you want to keep the PLC program in Step7 5.x.
So the only solution will be, to configure a passive S7 connection in the S7 in your Step7 project with the same TSAP you see in the TIA project when you select the S7 connection (10.02 for example) and then download the system data (CPU stop requested).
I can make you some screenshots of the settings if you need further informations.