I am assuming you have someone assisting/supervising you?
I would strongly advise against doing anything vacuum-related without a spotter.
People have died from experimenting with setups like this.
Other than that, you could try to get one of these giant bags and have someone vacuum you in along with the cake.
They are usually used for storing duvets/pillows/clothes and come with a seal for the vacuum hose.
"Vacuum storage bag" should yield plenty of results.
For example, found one in XXXL for <$20 in my country.
Looks tempting, if only I had someone to play with.
Just for science, if you have someone to watch over you and go through with it, please post pictures.
I mean ... who doesn't love cake?
Life's too short to pretend you're not into some kinky shit.