Try this. I think it is what your are asking.
Go to "enter exercise" page, there set the hours you challenge to 0. In your case you would set sleep to 0 and rest to 0. Then go to "+add exercise" and scroll down to other.Here you can rename and set your own values for sleep and rest.Now you can set the hours for these values.
Since you can personalize exercise times here you should, and then reset you RDI set up question page to show sedentary. The program will now base its recommendations on a sedentary life style plus any modifications you have added such as extra exercise, sleep, resting etc.
The Perfect Speed
"any number is a limit, and perfection doesn't have limits.
Perfect speed, my son, is being there.”
Chiang from "Jonathan Livingston Seagull