Once cold staking is activated it could be possible to stake using the Nano Ledger S, but that is up to Ledger themselves. Cold staking will be activated once 95% of the last 2000 blocks were produced by C# full node clients, i.e. staked through Stratis Core. I'm not sure what % we're up to at the moment, but I think it will still be some time before we hit the 95% threshold.

If you want to read more about the nature of the activation, it follows BIP-9: https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki