Math for Fine Motor Delays

As I have said before, my son is somewhere between third and fourth grade when it comes to most subjects, and math is the biggie that he is most ahead in.  He is currently doing multiple digit multiplication, like 4567 times 53.  The problems is, he is fine-motor delayed and has the handwriting of a preschooler, maybe a kindergartener on his good days, and he simply can't write small and neat enough to complete his worksheets.  Now, I was shopping at Target and saw these peel and stick dry erase boards.  They are like wall stickers that you can write on.  I came up with the idea of mounting one directly to the top of his desk.  It worked wonders and even has the large lines on it like a kindergarten writing notebook.  So I write each problem out for him larger and use another colored marker to draw columns so he keeps everything lined up easier.  He does so much better this way and I can even re-use the worksheets if I want to.  Next thing to conquer--Long Division.