We’d like to create a button in our support portal that says “ask the community”, and send the customer to the create new topic form. Since the customer at this point has already entered the title and description of the case they wanted to create, it would be beneficial if we could pass that through as a parameter to pre-populate that on the case creation form and prevent the customer from having to duplicate the input.

It seems that  fid=xxx sets the category, so maybe its possible with the other fields?