Guess a sub-panel with a 'main' and three branch CBs is a way to go.
The lock-out (if needed by placement) could be installed on the 'main'. (Two pole like may be used on an oven/range)
Oddly, I only came accross one job with this type unit about 2 years ago, the Ec was debating how to do this when I was there for a rough, and that job is still at a standstill ($$$$) Strange thing was the house has a 150 amp service!
