Hello,
I am not sure what is your requirement to not to upgrade ERP components on equivalent stack level of Netweaver systems. But this should be possible.
You should define your system as SAP Netweaver system in SMSY and it should not give ERP components while you will create transaction in MOPZ. But even if it select ERP components then you can unselect ERP components. As a result ERP patches will not be present in stack file.
But in order to keep ERP patches on same level, you need to provide vendor key during upgrade. For Vendor keys, you can get in touch with SAP Support.
Thanks,
Sunny