A blacklist, similar to the "Disable Items" tab in the settings screen. That way, you could do Dynamic Mode / Vanilla hands on for everything by default, but for a few specific items, turn off only vanilla hands while keeping the FirstPerson body visible. effectively, a "Disable Vanilla Hands Items" tab.
Hopefully this makes sense! I feel like it would be a great option to have to easily fix buggy issues with some other mods or modded items.