Several months ago I did some extensive web searches on fake backgrounds on various European sites. Lots of good information if you can patiently wade through it.
At any rate, I definitely saw some cages with plain coco-fiber backgrounds (i.e. with no sticks etc. embedded in it). I think the trick is to offset the more plain look with a lot of plants in the foreground, something your crested geckos should like anyways.
Try doing a google image search with both the terms flevopol and terrarium or flevopol and terraria. I think you'll find some examples that should answer your question.
BTW, flevopol is a concrete bonding agent sold in Europe. Keepers over there mix this bonding agent with coco-fiber and/or peat into a yogurt like slurry and just slop it on polystyrene. Most American keepers press dry coco fiber into curing silicone that is smeared on the background.
Of the one or two people who have tried both methods, I have heard that the concrete bonding agent is more desirable. There are several acrylic polymer emulsions sold as bonding agents in the US.
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Currently keeping a small collection of various Gonyosoma. Both G. janseni and G. oxycephala.