Remove time from date-time formula result; not using .toString()

Remove time from date-time formula result; not using .toString()

Dear Friends, 

I have date-time formula in a form to calculate certain date. 

Then, I have report (list type) based on this form, where I want to sort all records according to this formula field. 

The problem is: 
- To sort by formula field, I have to add this field into the report, and then only I can drag it into Sorting order
- Consequently, this field becomes visible and occupy too much space in the report. The problem is that it shows also time stamp, which is meaningless for me, like:   28/03/17 00:00:00. 
-  If it is only date, without time, it would be ok for me, but I can't get rid of time stamp;
- I can use  .toString() function to get rid of  timestamp; but then the result became String and sorted as a string, not as a date; for example, 18/10/2020 will precede 28/03/2017. 
-  I would prefer to keep this field hidden, but I don't know if it is possible or not, I can't find how to hide field in a report. Making it white-on-white color is not a solution, because it occupies real space anyway. 

Any suggestions?