This would be nice, but you can't. I've been wanting to do this too. Perhaps you should suggest this feature in the Feature Suggestions forum.
For now, I use the chr 160 in the window name, which is a non-breaking space in most low-ASCII fonts.
var %@ = $+(@name,$chr(160),with,$chr(160),spaces)
window %@ ...
...
The window above would display "@name with spaces" in the switchbar.