embroidery is done by computer... however, using a manchine
the computer will be hooked upto a machine that does the actual sewing and the computer will tell the needle where to go, based on teh image thats uploaded to the computer. we had one at my school. i cant imagine it will have advanced that much.
however... you need to get at both sides of the material so you cant stitch directly to the seats.
two options i can see.... either have the seats totally retrimmed by a pro with your choice of whatever sewn into the material, or... i can imagine anyone that offers an embroidery service for car seats knows a think or two about how to take off the material from a seat... so it might be a case of taking off the current 'covers' and stitching to that and then putting it all back together. theres no way you can get the logo or whatever put onto a different bit of material and sew that on somewhere. you will get a patchwork seat at it would look gash. unless it was like a centre pannel and you get that totally replaced
however unless there is a professionion lurking around on the forum... you arent going to know untill you actually speak to someone. however i do believe burple has some embroidery on his seats so speaking to Alaina might be a good idea
however my suggestions are purely based on logic