This is a great tutorial by Montrealconfections on making the stamp out of royal icing for cookies. If you could get some images of the computer and do it on plexiglass or something that is bendable to imprint around the cake and then work in the details. Just an idea hope it helps.
Edna de la Cruz has a tutorial on you tube http://www.youtube.com/watch?v=qqiNRkSQLf8
I have used round cookie cutters made into oval and it worked for me here's a link
I have stabilized cream with gelatine, the link below will give you an idea how its done. You do have to watch when the cream when whipping, too much and it can start separating and become butter.
http://allrecipes.com/recipe/stabilized-whipped-cream-icing/ read some of the reviews to give you a better idea
Here's a couple of sites, I haven't ordered from them though.
Allow the gumpaste to come to room temperature. Then take the amount you are going to be using and knead it with slightly greased fingertips. As you knead it will become pliable like chewing gum, color at this point.
Here's a good tutorial by Edna de la cruz