Okay, this is more or less OT MK1 specific, as OT MK1 uses a 6V/3A PSU and that makes it hard to find a solution, where as the other modern Elektrons have more plentiful solutions already available.

This looks to be a possibly great solution:

https://a.co/d/5sXcbzx

Some screenshots of the promo video shows the output DV voltage as programmable in increments of 0.1V, and starting all the way down at 3.3V.

I’m pretty happy with my Raptic TitanAC outlet battery, but it is much bulkier (and requires the OT PSU) so this might go in my Christmas wish list.