It seems odd to me, to attribute something to the translator rather than the original author, but regardless, I don’t believe you can change the author settings, differently between the primary and the secondary author fields in Endnote. The settings affect all the Author fields.
The only way to achieve what you want, would be to change the Translator fields in all your records to reflect how you want it to appear in this publication. – How many are there in your library? I guess I would copy them to a new library for safe keeping – and then edit them, so you still have the original ones for other publishing houses criteria.
If you edit them to Surname, AB et al – add a comma to the end, to make sure they are handled correctly in the bibliography.