If you put the mealworms into the bowl you use for the viv, and then put the calcium powder on top, and mix it all around a little, it usually does the trick. (well, it does for me anyway!)
Then, when you feed the babies, just take the mealies from this bowl to plonk in front of them, and they should already have a pretty good coating on them because they've been covered in it, and they've been wriggling around in it for a while. Some calcium will always come off, but you should still have a pretty decent amount on there.
I tried the misting with water, but just got a very sticky mess and half dead mealies which the leos weren't interested in!
Good luck!
