I have no personally done this before, but when I went to get an adhesive repaired on my convertible top I saw the guy there applying dye and heating it up with something that look like a hair drier at the same location. Seemed like a messy job, if the car is relatively new I'd probably move away from the DIY approch and move more towards having a professional do it, just because of the cost involved in recovering seats in the event that you screw them up. I think it was something like 50-100 dollars a seat to redo.