change apt-get default archives directory.

In /etc/apt/, edit a file apt.conf if it doesn't exist. In this file add the following:
Dir::Cache::archives "the/location/you/want/" ;
do not forget ;
In the director you want you must have similar lay out of directory. for example
/home/user/var/cache/apt/archives/
in the above directory you must have partial(director) also.
You can use the following to make the directory:
mkdir -p /home/user/var/cache/apt/archives/partial/
Then your apt.conf can be the following:

Dir::Cache::archives "/home/user/var/cache/apt/archives/";

Another way is:
aptitude -o Dir::Cache::archives "/home/user/var/cache/apt/archives/"
I did not try this one, though it is supposed to work.