touch file

There's lots of ways to do this. One possible way is to create a seperate makefile (e.g. touch.mk) which contains something like the following:

all: touch_myfile
touch_myfile:
       touch my_file.c
.PHONEY: touch_myfile

Then from the Windows control panel create the environment variable MAKEFILES which has as it's value the path to the makefile you just created, e.g. C:/touch.mk.

Alternatively you could just add the above content to app.mk in the Nios II kit.

I haven't tested the above, but something like it should work.