It's so hard, isn't it. The problem is that kids will then be really angry with him, and probably make him even more isolated.
Is there any way you could talk with the TAS in your area on giving his class a presentation on what the spectrum means, and how to understand the ways in which his mind is different? DS did this with the autism lead in the area in Year Two, and found it really helpful. I was scared shitless, to be honest, in case it was a disaster and he was isolated afterwards, but kids can be remarkably kind and inclusive as well as absolute little shits if given the chance, and somehow recognising that he is different, and how, did seem to help. It also helped how he felt about himself. That he was different, not wrong.
In an ideal world, this should be managed so it was an opportunity for all the kids to learn about difference, and diversity, and not a means to create resentment. Forcing them to play games they don't want to, with a kid they don't want to, will just make him more isolated, not less, I think. It's hard though. I really, really sympathise.