-u doesn't make sense in a local variable (because of the way mIRC triggers timer events and the single threadedness of script execution, -u can never actually trigger until the alias ends anyway). I assume this is to be used with -g, so if you need to set a global variable with an unset timer, why not just use /set? As far as "plain text" goes, just use $(text,0). If you want the features of /set, just use /set.
