Nope - just tested it. The only variable that currently works in the 'welcometocoursetext' string in the language pack is the course name.
I suspect the OP is either going to have to live without it, or (not recommended) alter the enrol/self/lib.php file.
I suspect the OP is either going to have to live without it, or (not recommended) alter the enrol/self/lib.php file.