A workaround would be for each output to have 2 keys, a spending key and a POS key.
This would allow users to upload their POS key(s) to a mining pool without that pool being able to spend their money.
Yup, But doing that also eliminates some of the incentive alignment arguments in the first place: E.g. that you'll take care of your keys, and not delegate (or do so only cautiously), not leak them, etc.. because your funds depend on them.
Sort of moot because the whole approach seems fundamentally unsound (or at least none of its advocates have stated a clear set of reasonable assumptions under which their system is secure (and where a centralized ledger wouldn't be)).
https://download.wpsoftware.net/bitcoin/pos.pdf