Hi Rick,
My suggestion would be allow BE to create it's own instance with SQL Express.
First, when you do update or install a HF your SQL services will be restarted if you are sharing your SQL server.
Second, if your SQL server goes down your BE database will also be down. Meaning to recover your SQL server you will need to install SQL Express to recover your SQL. Causing an extra amount of time to recover.
We are working on getting documentation for this.
Please let me know if you have any other questions.
Thanks.
Patty