I used Miralax for my last prep and thought it was the greatest thing since sliced bread (and I love bread!).
I used G2 and not the regular Gatorade (G1) because it is a thinner consistency and easier to drink more of it. If you can manage the gatorade, I hope you wil find this as easy as I did. I literally never felt nausous (and I get that easily---just the smell of black licorice makes me sick to my stomach). This was the first prep that I did not do...one glass for me, one glass down the drain.
I don't know if you can use other "approved" liquids. If you can ask your doc i would do that.