You need to make a business case. Jointly craft creative solutions . Really be open to new ideas. Spend time jointly brainstorming without commitment. Some people job-share.
Some people come into the office two days a week and telecommute the rest of the week.
When you do come to agreement, check each side's understanding. I would strongly recommend writing it down. The worse thing that could happen is that you have a different understanding of what the arrangement is. Renegotiate when appropriate. Set up monitoring and check-in mechanisms.