That's a easy base to cope being it's mostly flat. Cut your 45 degree back, flip it up side down and cut 22.5 degree back through the flat. Hog out the curve as well with the miter box. I use this with this bit to finish it. Cut out tool bit facing up, base of the tool against the stool I'm sitting on with my legs around it as a ghetto router table. Doesn't take me more than a couple of minutes to cope, although long pieces are annoying. Flap sanders on angle grinder are popular as well. Or a coping saw and a rasp if you wanna go old school.