Has anyone ever transported an already stacked cake with sugar paste flowers already on the cake? And if so, was there a special method used so that the flower do not break in transit?

I have several times. And no problems at all.

I took a large piece of countertop cut from the piece that came out when my sink was put in, set a piece of rubber grip stuff on that and then the cake on it. The whole thing sat on my lap and my hubby drove. The one in my photos with the gerbera daisies on it went about 100 miles with no problems at all. Well except that my thighs were asleep when we got there.

I transport as much of my cakes together as possible. And all the ones in my pictures have traveled with the flowers on them. I do take extras to replace if any breaks and to hide any misshapes that may form in the cakes. But most are done before getting to the reception.