I know this isn't a popular position to take in a linux forum but I'm a firm believer in using 3rd party bootloaders. I use BootItNG for no other reason than it's what I started with years ago. It's not free or open source but there are many more that are free. They all work on the same principle.
You create a small partition and install the bootloader into it. It then overwrites the bootloader in the MBR with its own code and acts like a traffic cop to direct you to whatever OS you want to boot that day. You will then need to change the way you install every new OS. When the installer asks where you want install grub you tell it to install it in the root directory of wherever you installed the OS. For example if you have installed "/" for Mint in say sda3, when the installer asks you where you want to install grub your answer is sda3. You do that with every OS you install and each one is a self contained entity.
The exception to this methodology is Vista. In vista I would use EasyBCD which isn't a bootloader, it's an editor for Vista's bootloader that allows it to boot "foreign" OS's.
If you where dual booting this concept doesn't make much sense ( except for Vista ). But as soon as you start booting 3 or more then it brings a level of control and simplicity to your machine.
Just my opinion.
For a list of third party bootloaders you might take a look at this: http://www.multibooters.co.uk/managers.html