Here is what you can do to accomplish this:
1. Enter your whole note in voice 1.
2. Enter quarter note rests for voice 2.
3. You can now enter the desired number of chords per rests that you created.
4. Double-tap the measure to open the select tool and go to "More" on the menu that appears.
5. Go into "Rests" and choose the option to hide rests.
You will now have one whole note being shown in the measure, with the desired chord symbols above it.