I find roundabouts utterly confusing altogether. Even when I'm driving in my car I feel like I am invisible to other cars approaching the roundabout. Seems like anything goes with these things! Luckily I do not have to ride my bike through one of these, but I would suggest taking the lane as you usually do so you can attempt to be seen as much as possible, but if cars do not want to yield to you, looks like you have no choice but to stop for them since the consequences of not yielding for you are obviously more fatal than for the driver. Unfortunately, doesn't sound like there is any easy method of using this roundabout. Sounds like the roundabout you use frequently has a lot of traffic, right? Is there an option to use a sidewalk through the roundabout instead? I wouldn't recommend "racing" through the roundabout to keep up with traffic though. That will only make it harder for you to stop suddenly if needed.