Have you looked into Explorers Club and Small Poppies? You don't necessarily have to test to be able to attend.
At that age, DD became a bit of a thought leader at kindy, which luckily the teachers were open to! She was full of ideas. Eg, she'd be big into making her own books, so they did a few book-making projects at kindy, and she was into phonics so they got in some CDs/worksheets which DD did with a few other interested kids. Perhaps you and DD can come up with a few project suggestions she can take in? Or at least send along some 'care packages' with her, something she's really into that she can work on?
The other good thing they had at DD's kindy was a separate room that only the 4yos were allowed in (at certain times of the day), with a computer with simple games, big kid toys like hard puzzles, construction equipment, special books etc. That was a great way of making the 4yos feel like big kids
