Load data using Data Services 4.2 with changing columns ?

Hi all looking for pointers on if/how it's possible to do regular Data Services 4.2 loads for data (in csv or excel format) which contains a key column along with a changing number of columns/data in different orders each time it is loaded & from which only specific columns need to be loaded? P.S. The file is generated by an API which cannot be changed.

i.e. Only want to load any of : key# plus ItemA and/or ItemB and/or ItemC and/or ItemD and/or ItemE,

Load 1 Contains:

key#,ItemA, ItemB, ItemC,ItemD, ItemE, ItemF, ItemG, ItemH

Load 2 Contains:

key#,ItemA, ItemJ, ItemK, ItemC, ItemD, ItemL, ItemJ, ItemE

Load 2 Contains:

key#,ItemJ, ItemB, ItemL, ItemK, ItemC,ItemJ,ItemF

Thanks in advance