I wonder if a way around this would be;

1. inclusion of 8/8 as a time signature (stay with me here...) and
2. inclusion of the option of a time signature being invisible when the chart is printed or viewed...

This would provide the option of including chords on any of the 8 eighth notes that appear in the bar, (which would be equivalent to all the beats and all the half beats). The invisible time signature would mean a musician reading the chart would not be confused by the workaround. You could put slash marks in the text field to indicate where the quarter notes fall for clarity if need be.

Apologies if I'm asking for something requiring fiendishly difficult programming. In theory do you think it could work?