Install packages in CentOS without root from non enabled repository

I need to install a high number of packages in a computer running Scientific Linux 6 (based on RHEL 6) for which I don't have root access. After much tinkering and internet searching I found this answer: https://stackoverflow.com/questions/36651091/how-to-install-packages-in-linux-centos-without-root-user-with-automatic-depen?newreg=471e1d62101f49198e06af008be75e6e Which almost solves my problem: it enables me to download the .rpm packages and install them locally. It makes use of the yumdownloader command which I believe will take the name of the package e.g. gcc and find the latest version in my enabled repositories (in my case 4.4.7) and download the rpm file. I can successfully install this file following the instructions on the link (I download all rpm files to ~/rpm then run cd ~/centos && for file in ~/rpm/*.rpm; do rpm2cpio $file | cpio -id; done and adding this directories to my PATH and LD_LIBRARY_PATH does the trick. However the version of Linux I am using has some very old (for my purposes) packages so I need to install a more recent version of these packages. I have never used a CentOS/RHEL Linux machine before so I am a bit lost regarding the package manager but I believe if I added a more recent repository this problem would be solved, but since I am not root I cannot do that. Is there any way to call yumdownloader so that it uses a repository of my choosing to resolve the package and download a more recent version? What would be the recommended solution to my problem? I know I could somehow find the required version for my packages and individually download the correct .rpm file from the web but this would be very time consuming, I would like to know if there is an easier way. Thanks.