I actually forked Eitr's fork and added this, but it's done with 2.2. I don't have enough time to merge it with 2.3 tonight but here's a link: https://github.com/deathrat/WGenerator/releases/tag/2.2-deathrat
There's now 2 tabs under Biomes, Generation and Painting. Painting will let you toggle painting mode, which will then let you place a biome by clicking.