short version: how should I top off the carboy on an apple mead, with about .5
to .75 liters to go?

Long version: above with addition. I really want to be careful with this apple mead.
In the future I will boil anything with apples in it to kill any wild yeasts and bacteria.
This time I used sulfites, but I'm thinking for the really low quality apples I grow, boiling
is a MUST (pun, hee, hee). These apples are fresh, but have lots of superficial fungal
diseases that would make them unmarketable. I can taste the wild yeasts in this 2 month old brew, but its
not bad yet, I think it may pull through, but I don't want to screw it up now. I really enjoy
the wild yeast flavors in my grape and berry meads that I use sulfites to sterilize, but I know how easy it can get out
of control in an apple mead. I'm paranoid because
the last apple mead I did turned out horrible, but it was my first mead and I tried a mediocre
recipe that involved sterilizing the must as an optional component. Yea, don't try skipping that. I just did a
second racking to a smaller carboy, but still need some more volume. I don't think water is
a good idea as it already has a watery taste to it. The SG was 1.1 when I started. I'm thinking
about adding honey water to give the yeast a boost? I don't have any compatible mead to add
but I guess I could add a white wine.