Have you tried modifiying the link to say:
[{{SERVER}}{{localurl:Special:Userlogin|returnto={{NAMESPACE}}:{{PAGENAM
E}
}}}]
This works! It is marked as an off-Wiki link, but I can live with that.
Thanks for your help. Please let me know if there's anything I can do
for you, like send you a Gmail invitation or help with some Wikipedia
edits.
Sincerely,
Matthew Simoneau