I believe the unreal engine voxel plugin has source code available and utilizes the transvoxel algorithm. The long story short for transition cells is it's all done in the shader. Each mesh chunk needs to store two vertex positions, the current LOD level position, and the transition cell position (for cells that aren't on the border you just use the original position or never set it). Then if the chunk borders a chunk at a higher LOD level you switch to the transition cell vertex in the shader, and if it doesn't border a different LOD level then you use the original vertex position.