Hey Steph,
I'm so glad to hear that your found a local support group for gifted kids somewhat nearby....that's wonderful.
Personally I think the 4th grade through 6th grade years are so important to establish that love of learning because a lot of hormonal and brain changes start to happen in 7th that make the social life so much more important - at least for myself and my kid. Think back to your own life and ask your son's Dad what things were like for kids in your generation when the go through that change.
We have a neighbor who homeschools by working nights so I know that can work, but it seems to me that one would need to be a very flexible and energetic person with an fairly independent learner for a child...and a way to lock up the TV and internet during the day. But it is great that your work has that option and your son does sound motivated.
What grade do the science magnet and IB programs start at? I think observing the classroom is the only way to know what they really have to offer. You can hear the 'selling staff' talk for 6 hours and walk away knowing less than when you started, but if you sit quietly for 45 minutes, you will know something real.
Meanwhile, it's a good idea to check out gifted summer camp options - SIG,CTY, etc. At the very least you may be able to get the light shining back in his eyes for a few months. Weekend conferences might be a good stop gap too. It was seeing how much happier my DS looked in these contexts that inspired me to take such extreme measures to give my DS a chance to relight the fire of love of learning.
Best Wishes,
Grinity