Well you would just play ...c7-c5 and answer d4-d5 with ...b7-b5. The fact that it loses a pawn is hardly a deterrent.
A "Benko-like" position from Nimzowitsch's Defense (1.e4 Nc6). Well, not really, since white still has a c-pawn....
Gharamian - Bauer, ch-FRA 2018
https://www.365chess.com/game.php?gid=4131912. This is analyzed in Bauer (2020)
The Modernized Nimzovich Defense 1.e4 Nc6!, pages 219-222.
an ordinary chessplayer wrote on 06/21/22 at 03:34:41:
I think some of the games in the book began
1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 O-O 6.Be2 c5 7.d5 b5?!. Benko points out some problems with that. In the line
1.d4 Nf6 2.c4 c5 3.d5 b5 4.cxb5 a6 5.bxa6 g6 6.Nc3 Bxa6 7.e4 Bxf1 8.Kxf1, at least white needs a couple of tempi to get organized on the kingside. Another line goes
1.d4 Nf6 2.c4 c5 3.d5 b5 4.cxb5 a6 5.e3, the idea being something like
5...g6?! 6.Nc3 Bg7 7.Nf3 O-O 8.bxa6 (
but see edit)
Bxa6 9.Bxa6 Nxa6 10.O-O d6 11.e4. At the cost of a central pawn tempo (e2-e3-e4) white gets smoother kingside development and saves on g2-g3. Playing the King's Indian version above gives white the smooth kingside development
and the central pawn tempo (e2-e4 in one go).
One advantage of the Modern Defense is you get a look at what white is doing before you choose how to create counterplay. You wouldn't play ...c7-c5 and ...b7-b5
no matter what. You would only play the Benko-like ...b7-b5 if white has done something strange. It won't be an exact transposition to Benko Gambit theory, but that doesn't matter so much since the Benko is a positional gambit.
Edited: Is 8.bxa6 accurate? I haven't looked at this in ... decades! Maybe white could wait with e3-e4 and a2-a4. Regardless, black should play differently at move five.