master of none is right - a 504 plan is used to remove the barriers so that the child can access the curriculum. It does not provide for changes to the curriculum such as enhancements.

Here is a good definition of an Accommodation: An accommodation allows a student to complete the same assignment or test as other students, but with a change in the timing, formatting, setting, scheduling, response and/or presentation. This accommodation does not alter in any significant way what the test or assignment measures.
Examples of accommodations include a student who is
blind taking a Braille version of a test or a student taking a
test alone in a quiet room. http://www.wrightslaw.com/info/sec504.accoms.mods.pdf

If accelerated work is typically available to kids in his school, and he meets the criteria to take part, he should be given access to that work along with the needed accommodations such as typing, dictating, more time etc. But, an enhanced curriculum in and of itself would not be part of the 504 plan. The plan covers the accommodations needed to access the program.