VERIFIED SOLUTION i
Product Feature: Printing/Output/Layout
There are no plans to implement tools that will give you this behaviour. Instead you can achieve this by using the guidelines and grid to align the boxes. Then zoom in closer to the Layout page and use the arrow keys to move a selected frame. e.g. you'd zoom in, select the frame on the right, and use the Left arrow key to move it towards the frame on the left. Using Shift+Left Arrow will move the frame a grid cell size at a time. Using just the Left arrow will move it a pixel at a time. You could start moving the frame using Shift+Left Arrow until it gets close enough, or use Guidelines to get them close, then use just Left Arrow to move it the rest of the way until the edges of the borders touch. Make sure to turn off Snap To Grid first.
UPDATED: April 18, 2017