urls with script/runner

i've got a rails app on my mac. i just figured out how to use launchd
to run recurring events on my rails apps via script/runner.

it basically checks the database for any tasks that are past due and
puts a list of them together in an email, with links to each one on the
site. being new to rails, i didn't realize that i couldn't use the
url_for method in my model. is there an easy way to generate urls in my
emails this way?