I didn't find a way to pass the URL as a parameter but I wrote a one line command that converts the url into mongorestore parameters:
CMD=`meteor mongo -U autocomplete.meteor.com | tail -1 | sed 's_mongodb://\([a-z0-9\-]*\):\([a-f0-9\-]*\)@\(.*\)/\(.*\)_mongorestore -u \1 -p \2 -h \3 -d \4_'`
$CMD /path/to/dump