I don't know if this will work with what you have there, but here's a trick I use to keep the humidity up on my cornsnake eggs. You might try it for yourself.
I always prepare the vermiculite/perlite/sphagnum moss mixture just like you said and place the eggs in the mix where they almost completely covered (3/4 or better). However, I then place a wet/wrung out paper towel on top of the eggs. This serves three valuable functions. 1) It helps keep the humidity up on the eggs as an added barrier against evaporation; 2) It serves as a very cheap hygrometer (if the towel is dry, it's time to mist!); and 3) I can mist the towel instead of the eggs, giving them the moisture they need without direct water droplets that might encourage fungus growth.
Again, I have absolutely no experience with the species you mentioned, but I cannot imagine that this would be detrimental. Check it out with a more experience person concerning your species', and let me know if this works for you as well as it does for me and my corns!
Good luck!
