Unless the 208 to 480 transformer currently being used is particularly valuable, or installed in such a way as to make replacement impractical, I would recommend getting a proper 208V delta to 480V wye step up transformer. I assume that this is a 480V delta to 208V wye step down transformer being used with a reverse connection.
However...If you have a 480V delta source, you can use a 'zig-zag' type autotransformer to derive a neutral. You ground this neutral and you will have essentially created a 480/277V wye source.
Usually these are only used for grounding, and are sized for fault conditions. However see article 450.5; I believe that you can use them to derive a neutral to supply loads; I think need some sort of overcurrent protection scheme that turns off the _entire_ system in the event of an overload of the zig-zag transformer.
-Jon