Y'all are making it too dificult!
1) Get the Plop boot manager and put it onto the USB.
2) Create a separate partition for EACH O/S ( I counted 7)
3) Copy the setup CD's to each partition.
4) Configure Plop to choose which partition to boot to.
All he wants is to be able to boot the USB and choose which O/S Setup to launch.
But, again, will 32GB hold it all? (Just barely, I think)