Here are some links about indoor bonsai. I would read them especially with an eye to improving the humidity around the tree. Of course, much of the info will not apply to a serissa, but it gives you an idea about how to help your serissa survive:
http://forum.bonsaitalk.com/showthread.php?t=14263
A simple tray filled with gravel or sand, sitting under your tree may improve the surrounding humidity. Make sure the actual pot that the tree is in, isn't sitting in water.
Good luck!
Joanie