Include a user in a dynamic group/assign a role/add a CoS attribute if some arbitrary other attribute contains the uid?

I can't quite see a way to do this. I have a load of nisnetgrouptriple attributes containing usernames in the form "(,uid,)" and I need to make a dynamic group or add a CoS attribute to enable a NIS unware app to check basic netgroup membership - everything just seems to fall short of being able to do this.