I use this every day too, I normally just stick to primary position in the middle lane on the approach to the flyover allowing cars who want to to overtake on the right to overtake while discouraging people from overtaking and then swinging sharp left in front of me to go off left to the roundabout, this then turns into the only lane of the flyover where I make sure I am in the middle blocking any dangerous overtaking. Luckily I can get up there pretty quick anyway so I've never had any trouble doing this.