The best thing for you to do is to use a VPN and connect through it. Besides the benefits of your ISP not knowing what you are downloading, you connect to some random server fooling MEGA into thinking you have a unique connection. Still doesn't solve issues with files that are just too big. A VPN may also allow you to connect to some other file repositories that may not have the same file size restrictions.
This doesn't always work, and rarely works with major ISPs (at least in the U.S.). Most ISP's lease you an IP address for 24 hours. Even if you disconnect and reconnect, if it is within the lease period, the head end will give you the same external IP address. All the file repositories used here check the incoming IP and meter downloads by that particular IP.