Chilling it overnight will help a lot.
I bag up all of our leftover BBQ at comps and since I don't have the option of chilling it and bag it while still hot and juicy, all I do is watch and as soon as the juice starts heading for the seal strip, I just hit the "SEAL" button to stop the vacuum. I may still have to wipe the top with a paper towel, but it helps keep most of the juices from getting all over the place.
They do have these LIQUID BLOCK BAGS
that you can buy, but I think they're probably not much more than having the paper towel in the top of the bag. I've never done that because I haven't needed to and I don't want the paper towel in there when I reheat the bags. BUT....I ain't knocking it either.