I'm not sure that would work. How would you know how much of the weight was being transferred to the floor? Also, it seems the mechanics would be quite different. Personally, I think I would substitute a different exercise like barbell rows or even more chin-ups/pull-ups.
The other thing you must decide is that since you can do one-armed rows with this new, heavier weight, would you not need that weight for all future back workouts? You'd only need one dumbbell, not a pair, so perhaps you can justify the purchase depending on your long-term goals. Otherwise, you'd just have to do the one-armed rows in the endurance mode and save strength work for other back exercises. Or do this exercise at a gym?