For OPT, the same level degree you can get second one with 20% chance
for special reason. (I don't know the details, but I know a friend who
is bio Ph.D. use 1 year OPT, then CS master use one year OPT.)
I think the best way is to try CPT, don't graduate now, pay some money
to school. Also I believe there are some other permisson,..
Talk with the company and univ..., sometimes they know more..
Good Luck