Andrew Poelstra is the second person I spoke with about this. Today he gave me permission to affirm here that he thinks CTV could be used for this purpose with Liquid.
He writes
What the watchmen need is super simple. “These keys allow moving the coins to a special timelocked staging area, from which the original keys can still pull them back” It’s basically a one-step vault.
In fact we literally implemented it in terms of unsigned transactions in an early version of liquid, but it was too difficult to keep them synced up and invalidated.
Given that he is short time (and a Delving Bitcoin account), he graciously allowed me to republish here.
So we have two independent attestations that CTV could be used to good effect on Liquid – hopefully that’s sufficient to put the matter to rest.