I used some JB weld type epoxy cement on the FLT80's support bracket. It was the easiest, most compact solution I found.
I scuffed the places where the bracket would touch the A4's center spine and put some of that epoxy.
After 12 hours of drying, It's securely held in place. There's space to fit an allen key to do/undo the screws fixing it to the reservoir.
Don't have a good photo of it glued in, but it went right about there:
Ended up having to switch that top rad and fans combo for a 30mm rad + 15mm fans as they would interfere with the GPU block.