You can define variables in your graph which you can set from the command line.
This is explained here:
Bulk Processing with GPT - SNAP - Confluence (atlassian.net)
In Python you can open the products you want to process and calculate the bounding box and then use it as parameter.
For doing this you can have a look at this example:
How to use the SNAP API from Python - SNAP - Confluence (atlassian.net)
And there is snapista. With this you can generate a graph and execute it as command line process.
But you would still need snappy to retrieve the geoinformation, or you read it from the metadata.