Britax Duo in center position in a CRV?

[BlockOfSheep]

Does anyone know anything about fixing a car seat to the middle isofix position?
I have 3 children (16 months, 4 and 6) and I am struggling to get a car seat solution to fit all of them...
Best fit seems to be Britax Duo in the middle isofix position (new CRV seems to have 3 possible isofix positions, 1 on each side as you would expect, or one using middle isofix hook and one hook from rear driver side near the middle)
However, Britax website states that Duo can only be fixed to either side of the car, which means I struggle to fit eldest child's booster into the car as the seatbelt fixes behind it.
Araragh!
If the car seat has been fixed, and appears to be secure, is it not then secure?
I am very confused...