Yes you can do 90+10 online. I did it the other day and it worked well.
Go to WDW official site and navigate to the dining page. From there find the restaurants your interested in. There should be a links to make reservations for each one. After you click on those youll find another link above where you are prompted for date and time to retrieve your reservation. Click on it and enter your reservation number and phone number. This will allow you to book +10 days out from your 90 day mark.
You can start booking at 6 AM Eastern Time on the 90 day mark. I live in Wisconsin so I was able to start at 5 AM Central. Keep that in mind for those of you who live west of the Eastern Time zone.