Giving command line parameter to textconv command?

Some text documents in my repository is encoded in EUC-JP and I have this line in my .gitattributes file.

	*.txt	diff=eucjp

and these two lines in my .git/config file.

	[diff "eucjp"]
		textconv = nkf-w

And I have ~/bin/nkf-w script that is executable.

	#!/bin/sh
	nkf -w "$@"

The command takes a (Japanese) text file and converts it into UTF-8 (it guesses the input encoding).

I need this extra script because setting 'nkf -w' for textconv like this

	[diff "eucjp"]
		textconv = nkf -w

gives an error.

	% diff --git a/hello.txt b/hello.txt
	index 696acd7..f07aa1a 100644
	error: cannot run nkf -w: No such file or directory
	error: error running textconv command 'nkf -w'
	fatal: unable to read files to diff

Could you fix textconv so that it can be given parameters?