One question about nios2_multiprocessor

If you expose the reset lines to the subsiduary processors and connect them to (say) a pio slave that the main cpu has access to you can load a single image that contains code for all the cpus.

Once the first cpu has initialised any shared areas, it can take the other cpu out of reset.

You probably can't use the jtag debuger or uart on the other cpus.

If you are using theother cpus for simple tasks the code required can be tiny - ignore all the altera supplied support, just initialise the %sp and %gp registers and jump directly to the user C code.