do the pool/book work at home, then finish the job insan pedro with a referral as described above.
pretty much all the dive shops listed at: http://AmbergrisCaye.com/diving/
offer those classes...
thats what our whole family has done. we take the class right before we go down, then when the rest of the class does their open water dives in 40 degree water with 4 foot visibility, we head to Belize!