http://support.apple.com/kb/HT2534?viewlocale=en_US&locale=e...
(But, man, do I hate such kludgey workarounds.)
EDIT: Seems to have worked fine - download in progress, and I didn't actually complete installation of the free app (AFAIK; I did have to enter tombstone info, but I can live with that).
http://support.apple.com/kb/HT2534?viewlocale=en_US&locale=e...