Start simple and build it up.

I beleive there is a Finnair HEL-MIA that will price into a lot of these ex-EU fares. But it's easy to put things in a way Matrix can't calculate when you use a simple return, so you will need to break it out into multi-city mode to do anything tricky. Make sure to put in the specific flights you want (includng the airline you want for it) for some of the sectors once you have found ones you want are trying to fit them into a priced up ticket, that reduces the amount of work Matrix needs to do.