Emma,
I think the relevant part of the sped regs for ESY in your case is probably this:
"Students must be considered for twelve-month special services and/or programs to prevent substantial regression if they are students receiving other special education services who, because of their disabilities, exhibit the need for twelve-month special service and/or program provided in a structured learning environment of up to 12 months duration in order to prevent substantial regression.
Both quantitative and qualitative information should be reviewed by the CSE to substantiate the need for providing such services and programs. A student is eligible for a twelve-month service or program when the period of review or reteaching required to recoup the skill or knowledge level attained by the end of the prior school year is beyond the time ordinarily reserved for that purpose at the beginning of the school year. The typical period of review or reteaching ranges between 20 and 40 school days. As a guideline for determining eligibility for an extended school year program, a review period of eight weeks or more would indicate that substantial regression has occurred."
If I recall correctly, you may already have data that supports the regression/review period tests.
Using your existing eval reports, you may also be able to get two years of free Orton-Gillingham through the Scottish Rite Masons. Check here for locations and contact info:
http://www.childrensdyslexiacenters.org/Home.aspx