Hi Jeff.
I have had a similar problem with my main page. I have a forum where I post news and I want all users to be able to reply to my posts. I assigned all the users the student role and ... voilà ... everybody was assigned to every course. I disassigned the student role and after some tries I think I've found a possible solution (I'm just testing):
I've created a new role, with name "user", that has the same permissions than the guest role, with this exceptions:
In core system:
LEGACY ROLE: Guest => inherit
LEGACY ROLE: Student => allow
In course:
View courses => inherit
(this is the one that automatically assigns all users to all courses with the "allow" value)
In forum:
Start new discussion => allow
Reply to posts => allow
Create attachments => allow
Delete own posts (within deadline) => allow
I think it works. But I have to do more testing.
If you need the "choice" activity, I think you must change, in choice:
Record a choice => allow
I hope it helps.
Roger