I have the Zhumell version of the GSO Barlow. I should just screw that into my 14 ES which would give me about the same mag and field as the 9. I have done that before with the 14.
I think you could do that with very good results. But we always end up wanting more EPs rather than less and also we always second guess whether the barlowed views are "good enough" compared to non-barlowed. In my case, with the ES100 9mm, there isn't a 5mm yet, so I don't mind barlowing it to 6 or 4.5mm where my astigmatism doesn't show up.