Disabling Bluetooth Absolute Volume on Ubuntu 25.04

I have a pair of Sennheiser Momentum 4 noise canceling headphones. They of course work over Bluetooth, the protocol that has more warts than features. One of these warts is "absolute volume", which purports to tie the volume of the headphones and your source device together in the name of convenience. The problem is that with absolute volume, even the lowest volume setting on my laptop is…