I had a similar problem with my 5-year old ACF last winter.
The only amphibian-experienced vet in my area was out of town, so I had to see what I could do on my own. I consulted a herpetology website and based on that, I raised the temp in the aquarium a couple of degrees and fed a largish meal to boost metabolism and stimulate gut movement. It did work in my case, but it could have been a disaster if she'd been unable to pass the impaction. If you have an amphibian vet, that's always the best option**. By the time my vet got back into town in order to give her a checkup, he said she was back to normal.
I would say that if your frog is that inclined to eat sand, perhaps keep him/her in a tank without substrate until s/he's a bit bigger. If the sand eating is secondary to feeding (i.e., while pulling food in the mouth sand is also pulled in) perhaps you could switch to a non-sinking food to alleviate the problem.
** Disclaimer: Any approach I took during my frog's impaction was undertaken because my vet was out of town.. I am simply stating what I did. It is not a treatment. If you want true treatment, please seek veterinary advice.