I wish there were a simple solution, and I'm not convinced there necessarily is a way to avoid a rise of a radical...other than if it's not an issue in the population and if it's indeed not an issue that is relevant. In that sense maybe what's more important is the social base. If people don't see this as an issue, and if you can create a society that is based on mutual trust and co-operation, then it won't have to become an issue. That is maybe more important.
If there are tensions in society that are not being addressed, and people are not able to give a voice to them, or people are in insular communities, then a more proportional system may—and I stress again, may—give rise to certain radical right parties. But this should not be the only consideration of political party change, I should emphasize that.