At one time, and in limited cases, SCCA has allowed roll bars to be braced at the height of the stock shoulder belt attachment point.
I think it was for Solo only, and I am fairly certain that some other specifications were included.
If my memory is accurate the two cars specifically listed were Porsche 914 and Toyota MR2.
Thanks for the lead, I started googling MR2 roll bars:
A Roll Bar detail ties into something right at the shoulder belt: Techno Pro Spirit Rollbar
A low angle "rear brace": FS: Silver 01 MR-S - $7000
Another style with a very low angle rear brace: New Roll Bar Supplier NOW WITH PICTURES - Page 23
Seems like we could create the same geometry with the Solstice body, but instead of a baby short low angle rear brace, it would be attached directly to the wall behind the seats.
I would say the application I have in mind would be for the street, but I see rules as the minimum best practice. In the 2017 Solo rules, Appendix C section D it says:
All roll bars must be braced in a manner to prevent movement in a foreand-aft
direction with the brace attached within the top one-third of the
roll hoop, and at an angle of at least thirty degrees (30°) from vertical. It is
strongly recommended that two such braces be used, parallel to the sides
of the car, and placed at the outer extremities of the ro
I interpret this as, the Solstice humps are within the Top 1/3 and a brace directly to the rear wall is effectively 90° from vertical, exceeding 30° from vertical requirement