Exercise Substitution for Back Extentions

I am going to try CW’s Singles club program. On day one he has back extentions as the second exercise but my gym has no equipment for back extentions. Does anyone have a good substitute idea?

Substitute back extensions with Romanian Deadlifts utilizing dbs or a barbell.
Movement: stand upright with a db in each hand and resting against the front of your thighs. Suck air into your gut, push your hips back, and lower dbs until they are just below knee level. Once you reach the bottom, squeeze your glutes together and extend back to starting position. Obviously, your lower back should remain tight and arched throughout. There are various pics of this exercise if you perform a search.

Thank you Chad, I will do that.