how to deal with Dual boot pendirive or flash drive

hello friends everybody knows that we are able to make pc or laptop to work in dual boot either side by side or in one into another. The second thing is that we mostly uses the pen drive or flash drive for the bootable device to install the os in our system. sometimes the system will not get boot from the direct bootable device then in that case we uses the cmd and make the primary partition in pendrive and make it bootable and our system will now able to take boot from the device.
so these are the normal things we uses but i want an other thing. My question is that is it possible to make pendirive or flash drvie or the cd or dvd as a dual bootable device. Or in other words i can say that i want device which is bootable for two os like windows 7 and windows 8 . and when i try to boot it in system it takes my choise of which i want to install to the system. I want the same booting thing as in system either pc or laptop which is used in the pendrive or flash drive ot cd or dvd.
The only difference is that system in dual boot is used to get two latform for work on the same but i want the same thing from a pendrive the difference is that now i want to install os from dual boot of my choice.
Guys if it possible and if it does then how can i am able to do it. I think its whole is the engineer's community and engineer's are just for doing new things so want to do it any body can help me? pls giv me sugestion for doing this and if some already able ot do it then pls share the procedure to do it.