Scott, I'd check with the vet on that one. It's going to depend on exactly why your gecko IS impacted. In other words, exactly what food are we talking about? The only impaction we know much about is from ingesting sand used as substrate, and that, unfortunately, is often a death sentence. (Surgery might work, but you'd need the Mayo Clinic of herpetology vets to handle something that delicate.)
We've never used anything but live crickets (they won't touch roadkill, or at least we've never seen it), and they've always passed those just fine as long as they also had water to drink.