Is there any way to boot from iso while running system from live disk?

This is bit complicated question let me explain what is expected: I know that we can add GRUB menuentry with location of ISO file and boot from ISO using GRUB entry. (i.e [this](https://askubuntu.com/a/340171/256099) method) But suppose that: - I've ISO file of a GNU/Linux (say Trisquel 7.0) stored in computer (hard-disk) say at /dev/sda3/ - I want to install it on /dev/sda4 - I've Ubuntu 14.04 installation (bootable) disk from which I can install or try the live system. - Consider I've no operating system installed currently or installed system is crashed/corrupted (nothing to do with current boot-loader) The question is: With the Installation disk, running live environment (say try without installing of Ubuntu 14.04), Can I boot from the ISO (of Trisquel 7.0) from /dev/sda3 and install that system on /dev/sda4? How do I? Note:I agree that it is better to create/burn live disk/USB of the system I want to install from iso but If there is no disk/usb available right now then Can I do such operation mentioned in question? I think there is one possible technique: Install GRUB from (Ubuntu's) live environment on HDD pointing the path of ISO (Trisquel) that I finally want to boot from! How to?