I dont feel it should be done. They dont just get impacted because they are eating on a substrate, but because they constantly taste their enclosure. Its like a snake and them flicking their tongue. The gecko can get the aspen on its tongue when it licks around is enclosure and then accidentally injest it causing impaction.
I wouldn't do it because feeders tend to burrow into loose substrate like that. I have found that in my display tanks the best substrate is either a low pile outdoor carpet (comparible to Repticarpet) or natural slate tile. I just use paper towel in my rack.
And, as always, with loose substrate you always run the risk of impaction.