Tipster Tomislav Vargek has added another option to a previously submitted tip (#3727, by Kent Cooper) that already contained three ways to join text and mtext into a single mtext object. Tomislav has added an option to stack text into fractions or other stacked text divided by a horizontal line.
Start by loading the LISP file. The functions originally defined in tip #3727 are still present; they are 1MT0, 1MT1, and 1MT2. The new stack option function is 1MT3. Be sure to only select two text or mtext objects to combine.