Very trivial.

Unpack your cursor package to ~/.icons/.

The directory structure should be:

~/.icons
~/.icons/theme_name
~/.icons/theme_name/cursors

Create a symbolic link between ~/.icons/default and the theme_name and restart X.

ln -s ~/.icons/theme_name ~/.icons/default

If you have any issues, remove the symbolic link:

rm ~/.icons/default

create a ~/.icons/default directory

mkdir ~/.icons/default

and insert the following file (index.theme) into the ~/.icons/default directory:

touch ~/.icons/default/index.theme
vi ~/.icons/default/index.theme
   1 [Icon Theme]
   2 Inherit=theme_name

Done; easy.