Something like this might work, a lot would depend on how how fast the supply of HBD could be changed as a result of more people moving their liquid Hive into savings to generate HBD. From a speed of conversion view, the Hive->HBD conversion operation will be able to create more HBD with less Hive, so it should be easier for Hive holders to stop any upwards swing of the peg with the conversion operation than using your proposed method. It's also much easier to implement the conversion operation.

Still, I'd say it's an idea to consider for later, along side other proposed ideas like the collateral idea. It does serve some secondary functions, that neither collateral idea nor the conversion operation really serve: a reason for Hive holders to keep their Hive off of exchanges and a way to earn some staking rewards while providing a useful service to the network, even if you don't want to participate in curation voting.