I have graduated 5, all girls. (Two of my boys dropped out, so they didn't get a party) My next son, 17, is now done and I'm trying to work on a party for him. His may be a little different than my girls, but we'll see.
What we did for each of the girls was have a "Graduation Open House/Reception." I made invitations with a high school picture and sent them out. They all had senior pictures made, not professionally, but just each one singly by a friend or family member with a nice camera.
Then I made them each a scrapbook/yearbook full of school memories and events we had done all through their homeschooled years. I also had empty pages for the books that were on our reception tables with pretty pens for guests to sign. Just like in *my* high school yearbook.
The other thing I did that was nice was make a "wall" full of memorabilia from different things they did and things they enjoyed. For instance, my oldest daughter was very involved in our local Christian theatre at the time so we had the awards she had won and some theater scrapbooks on the table. One of my daughters took a horticulture elective class and loves flowers and such. Her table was decorated with flowers and unique things like that for her.
We had cake and refreshments. One daughter had a film maker friend, so he put together a slide show with music for her that we all sat and watched. We also were into playing frisbee with this daughter, so there was a big frisbee game going on in the yard. And poor kid, but she got hit in the face during the game!!!
My son is a huge volleyball fan AND he wants a diploma (none of the girls cared), so we'll have something going on for those interests.
None of mine wanted a "ceremony" either, just a fun afternoon/evening that was for them to remember and for us to honor them with.
I also left pages in their yearbooks for pictures of their graduation party.
So be creative, make the event match their achievements and interests and have fun.

Vicki in SW. MO.
Mom of 9 (ages 14 - 35) and Grammy to 7
14 ds - Finished CTC, RTR and Rev To Rev; MTMM - Fall of 2016