I have a request for a stand up martini glass cake for a gal's 21st birthday. I have the idea to carve the top of the glass out of cake then maybe using a tall round piece of styrofoam covered with fondant for the stem of the glass. making a piece for the bottom out of fondant to look like the bottom of the glass. I have just started thinking about it so I'm sure there is a ton of perfecting the idea. I would really appreciate any advise or ideas anybody has. I have not agreed to make this cake yet I told her I will have to do some researching before I make a final decision. I know I need a lot of supports I was also thinking besides all of the other supports I will need, doing 1 final dowel down through the entire cake into the styrofoam stem of the glass. I think that will give it alot more stability. What do you guys think? Am I on the right track? Thank you all.

I would not use styrafoam for the stem. I would use PVC like 2-3 inches in diameter. Styrafoam is not strong enough. Then I would get a plumming flange and cut a square of MDF and attach. Traveling with this cake is going to be the scariest thing you ever do. I would also carve the lower part of the cup part out of styrafoam and stack a layers of cake ontop for the final few inches.

How many servings do you need?

Here is a cake I did... perhaps it will inspire you for something else. Sorry I can't be more help.
Good Luck....