I believe this could be worked around simply by re-enabling that field and allowing the user to specify an email there by hand, making a note that the OpenID provider's email is used by default.
+Here's the dumbest [[!taglink patch]] that actually fixes the problem for me:
+
+[[!format diff """
+diff --git a/IkiWiki/Plugin/openid.pm b/IkiWiki/Plugin/openid.pm
+index e3b9982..df87ba3 100644
+--- a/IkiWiki/Plugin/openid.pm
++++ b/IkiWiki/Plugin/openid.pm
+@@ -104,7 +104,6 @@ sub formbuilder_setup (@) {
+ size => 1, force => 1,
+ fieldset => "login",
+ comment => $session->param("name"));
+- $form->field(name => "email", type => "hidden");
+ }
+ }
+
+"""]]
+
+It would probably be better to add a comment on the field as indicated above, but it's a good proof of concept.
+
Any other ideas?