I can think of two possible ways to deal with this.
1) Create the risk register in Excel and attach this to the project template, so less integrated with Clarizen.
2) From the project: Create a temp risk (otherwise case panel is not available), Import a CSV file of generic risks, manually add risks to the project (this doesn't seem to automatically happen?!)
Ideally the generic risks themselves would be maintained in Clarizen instead of an Excel or CSV file, then could be assigned to a project via a workflow or loaded with a template.