best way to close the slot is a toothpick cut to size and glued in place. Then you can position the mini, and glue it to the base itself using plastic cement. It takes a while to dry, but the bond is rock solid, and it can work quite well on tiniest connections.
I just got my mei feng crew, and the rail golem, and the plastics look quite similar to what i'm used to from scale models. I would recommend everyone to use Tamiya plastic cement for these miniatures:
http://www.hobbylinc.com/htm/tam/tam87012.htm
or
http://www.hobbylinc.com/htm/tam/tam87038.htm (i personally prefer this one)