It is not as straightforward as it might seem at first, because a number of distros have different methods of booting, and allowances would have to be made for each of those when placing the various OS files for each distro in the filesystem.
Yes it can be done ...... it is several years since I tried and succeeded to a certain extent.
Some distros are easier manage than others.
The main requirement, as far as I remember, is to find the info for each of the distros you want to include, arrange the OS files as specified, and finally write a boot config file with suitable options for each.
regards.