The coco fiber should be fine to compost. Just keep in mind that if your frog needs medication, them that "batch" of substrate might not be a great candidate for composting because it will have some traces of the medication.
If you're worried about impaction, I would look into bowl feeding your frog. Just get a smooth-sided bowl with sides about 2" tall and the crickets won't climb out. That way the frog isn't feeding on top of substrate.
As far as not wanting to waste substrate materials, you might want to look into constructing a living vivarium. You just need a drainage layer of clay aggregate or a constructed false bottom, then a thick layer of ABG mix or similar substrate. You can top this with leaf litter to Eddie impaction concerns. The addition of springtails and isopods gives you a clean up crew that breaks frog waste down into fertilizer for live plants. It's like a mini ecosystem that doesn't require substrate changes, so there will be very little ecological impact.