I also am the mother of an identified gifted child who also has ADHD. Our other two children are also identified as gifted, but without the complication of ADHD. I don't know which school district you live in, but there might be a director of services for gifted and LD for the district, and talking to that person might be helpful. If his ADHD is truly getting in the way of his learning, and is disruptive for the classroom, he may qualify for an IEP (individualized education program), which will entitle him to special consideration. It is easier to get in elementary school than in middle school, so that may be something you want to consider over the next few years.
You do not need to wait for the district-wide testing in order to have your child evaluated for identification as gifted. Psychologists and LSW's also can perform that testing privately (although you do have to pay for it). Your district also may be willing to test him separately from the other children. For a kid with ADHD, that may provide a better result since ADHD can also affect test performance! If you have evidence of the giftedness from test results, your school may be more willing to work with you.
As far as what you can do to help him now, the enrichment ideas at home are great - but they don't have to be so formal, or even so disruptive to the lives of the littler kids! We found that the public library is one of the best resources - go hang out there after school. Good libraries will have activities for your little kids, and most librarians love to help bright kids find books to learn more about things they love. Ask his teacher if he can take a book to school with him, and read at his desk when he is finished with his classroom work but is waiting for his classmates to catch up. Or, does he like to draw? If he always has a sketch pad and pencil, he can do that when he is bored. It's the boredom that drives the bad behavior...
Don't give up on the medication front. If the medication was helping but isn't any longer, it's possible you need either to adjust the dosage or try a new medication. It takes a lot of time, effort, and patience on your part to find the right medication and the right dose - and there is no guarantee that the same medication will work forever. My son, who is now 14, probably tried 4 different meds until we found one that worked without too many horrible side effects. Your pediatrician will be able to help with this. Try to chart his response to the medication - if you can tell when the effect wears off, make a note of that - it can help to determine dosages.
Last of all, there are schools which are specifically for kids in your child's situation. If the public schools can't help, that may be a route to explore. We finally removed our son from public schools in the middle of 8th grade, and have him at a private school. The difference has been huge. He is learning to manage his ADHD and is finally achieving near his potential.
Good luck!