Jim, What is the proper way to ask the VA for an SMC rating of Level S?
You don't 'ask' for a disability rating, you apply for it by clearly and logically demonstrating that you meet and/or exceed the published criteria for such an increase. Housebound Benefits (Category S) have very specific requirements that you'll find here.
If you are sure that you meet those criteria and that you can support that with your medical records, you will simply make the application as you would for any disability benefit. Once you've done that you'll be notified that your claim is being processed and you'll be scheduled for a C & P exam where your application and records will be reviewed.