Placing guideline in the middle of two other guide lines

To create accurate symmetrical drawings, it is often required to create a guide line exactly in the middle of two other guide lines.

It is currently possible to do this, but it is convoluted. You can either double click the existing two guide lines, note the coordinates, calculate the middle of it, and then place the third guide line in the middle using exact coordinates. Or you can create two line objects, place them at the two existing guide lines, then create a third line object, and use Align and Distribute to place it in the middle. Then convert the third line object to a guide line.

There must be an easier way to do this. Perhaps make Align and Distribute work for guide lines as well, instead of just objects?