I have a Grid that is bound to a 'banded' datasource. Is there any (easy) way to go from the nested/banded data into a single band or 'flat' data?
No, there's really no easy way.
Depending on your data source, you might be able to modify it by implementing ITypedList.
You might be able to use Unbound columns in the grid that you populate in code.
Another method would be to use an UltraDataSource and load the data on-demand.