Hi Guys,
Normally we use to install mbstring and other modules using cPanel easyapache tool and as you all know, it will take 20-45 minutes to complete. Suppose you just need to install mbstring. Then you don't have to run the easyapache script. Simply follow the steps given below.
cd /home/cpeasyapache/src/php-5.3.21/ext/mbstring/
./configure --with-config=/usr/local/bin/php-config
make && make install
That will install mbstring in your system.
Give it a try!