It's all been done! Wallets molded into the sidewall inflated and as far as i can remember, worked perfectly. It was before my time, so will take time to research.
The problem was the loss of retardation. Having said this, I can't help feeling that it would save a lot of rubber if a spin-up was optional. 12,000 feet of concrete and time to have lunch between touchdown and turn off, would save a lot of bucks if there were no rotational impact, but then we would be back to a mechanical system -- with all the above disadvantages.