a2 folders
 

is there a way to use a a2 embossing folder on a 5 x 7 card?

Try turning the folder sideways - if it's a repeating pattern that can be used horizontally, you can run the piece through twice. Line up the top edge with the side of the folder for the first pass; for the second pass, line up the edge of the folder with the edge of the embossing. You may have a slight line at the joint, but you could cover that up with another layer or ribbon if it's very obvious.

You can sometimes avoid that line if there's enough "overlap" on the pattern - put the partially embossed piece in so that the embossing lines up with the pattern on the folder. Then when you run it through the machine, stop rolling just before you reach the edge of the folder and reverse it out. If you don't "bump" over the edge of the folder, you won't get the line.