While the _equipment_ only requires the three 'hot' conductors, is the supply a 460/266V _system_?
As I read 215.11/210.9, you can use autotransformers to derive a 480/277V feeder or branch circuit, even if the load does not _use_ the neutral; the key is that you are not deriving a new neutral conductor, but instead keeping the same neutral between supply and load side of the transformer.
On top of this, I'd guess that a very sensitive system (designed for 480V but can't tolerate 460V) is also sensitive to the L-G voltage anyway; if the source is ungrounded I'd look into an isolation transformer to fix that as well.
Ideally you would use a set of 3 transformers, each rated 266V:11V in a wye autotransformer configuration to boost voltage. Those won't be available.
But you could use common 240/480 : 24/48V transformers. Use the 480V primary at 266V, that makes the 24V operate at 13.3V. In a wye configuration that would boost your 460/266V system to 483/279V. You would need 3 1kVA rated transformers.
-Jonathan
