Alright, thanks. I was just wondering if it was feasible or not
The answer is yes, but the choice of AVR's is limited to ones with enough flash, and a reasonably similar USART (to minimise the amount of code you need to rewrite).
Is their a specific reason why it must be the Arduino bootloader, rather than any other AVR bootloader?
You might want to look at V-USB. Which goes one step further and implements a USB interface on ordinary AVR's which don't have USB hardware.
There are a set of V-USB-based programmers which don't need a USB chip. One uses an ATmega48 so that it can program itself over USB, without a USB chip.
I would tend to go with BenF, and just use an ordinary programmer unless you have a special reason to do it differently.
You could make yourself a very low-cost USB programmer using the technology at V-USB.
HTH
GB-)