In one of my laptop partitions I've got a variant of Ubuntu Lucid (called Deepin) installed. I used Unetbootin to install Ubuntu based distros inside that partition a few times (I mean, one distro at a time). Each time Unetbootin basically added one or two directories containing the live data of the distro and added boot entries to the Grub menu. On rebooting after installing the distro this way, I select the entry "Unetbootin" on the Grub menu will run the distro the same way as running the live CD or USB of the distro, but much faster.
In case I want to delete the installed distro, I just run Unetbootin again within my Lucid variant (Deepin) and I'll be asked if I want to remove the installed distro. On confirming, the distro will be removed (the added directories and Grub additions) right away.
I have tested a few distros this way and I'm very happy with it. But I must make it clear that I haven't tested non-Ubuntu-based distros this way; and I recall reading somewhere that some versions of Unetbootin may not work this way.