In the authoring tool I've been able to create 2 vertical-stacked components in a single block by opening the same page editor in two browser tabs (in Chrome at least).

Open an empty block and make sure it's appearing in both browser tabs. Add a component to the block in one tab, then without refreshing add your second component to the empty block in the 2nd tab. Hit refresh (on either) and the components should appear vertically stacked in the block.