How can rotamers of alpha-keto esters be named to distinguish between different geometries?
The IUPAC recommends s-cis and s-trans for the rotamers of conjugated dienes. 



The nomenclature derives from having a "cis-like" or "trans-like" geometry about a sigma bond. 

I feel like something similar should be appropriate, however that same IUPAC link recommends E/Z or sp/ap (syn-periplanar/anti-periplanar) for the N-alkyl amides (5,6). 



Amide 5 would be Z (but ap w/r/t alkyl groups) and amide 6 would be E (and sp). E/Z is less ambiguous in my opinion.

Ketoester 1 is E, and ketoester 2 is Z. I suppose that ketoester 1 is also ap and ketoester 2 is also sp.