Follow the same strategy as "Every able body". Summon a rifleman during a bonus round to upgrade archer allies. Riflemen are distinguishable by the fact that they cost 10 upgrade points to summon, and their picture is a unit holding a rifle. Putting these on the field, then spamming archer to spawn will automatically upgrade the archers. Make sure you are able to keep the rifleman alive by summoning allies ahead of him to distract the zombies. Again, don't worry if you don't do this in one wave, it can be done over multiple waves but can easily be done in one wave.