download elf without full nios install

Sorry I gave just an element of answer, this is not exactly what you expect (as you said)

If the NIOS II SBT can download to the board and then starting the board, it can be done by command line.

In Nios II sbt, when you download software through JTAG, you have a (very) long command line that appears in a window

See something like nios2-download --go ... .elf

Sorry again, I don't have the exact command right now, but it should help you.

EDIT : you must install quartus standalone programmer (over 800mo !!) in order to get USB Blaster working, JTAG working (to communicate with the NIOS II processeur).

You could try to copy nios2-download and cygwin1.dll from a Nios II SBT to <Quartus II Stand-Alone Programmer Path>/bin of the standalone computer.

manually append <quartus ii stand-alone programmer path>/bin to path environment

and test.

Good luck and tell us if you have succeeded.

Regards