I set up one of these. So far I love it (and there is only LR and LS in it). I have a Nassarius Snail (hitchhiker) and 2 mini feather dusters (hitchikers). I added about 1.2 LBS of LR and 1LB of LS to the tank. .2lbs of the LR is in the filter, and I will be adding macro pretty soon.
I have yet to test it, but I'm pretty sure you could make a mini drip system for top-off. I currently loose ~6oz (3/4 cup) of water/day (I live in AZ). When I worked at a LFS a few years back they had a drip system for chamaeleons. It held a cup or two of water. You'd have to measure your evap rate and toy w/ the drip rate until you got it right, but I see no reason why this couldn't be successful. If set up right this would help keep the salinity stable or at least offer a "vacation solution".
System parts: plastic jug w/ airline and plastic flow regulator (an easy DIY project, silicon would be VERY handy). Possibly use an "IV crimp" (I dunno what the heck they are really called) for flow regulation.
If someone experiments with this I would love to know. I will be, but right now I have only a snail that likes to crawl up my intake (@#%&!) and the feathers. Once I add coral I will be doing this and I'll get back to you on it.