Great question!
It's not yet possible to do this via the admin interface, but a bit of PHP can do the trick. In qa-page-home.php, insert the following code:
array_unshift($questions,
qa_db_single_select($qa_db,
qa_db_full_post_selectspec($qa_login_userid, 392299)
)
);
...after...
$questions=qa_any_sort_and_dedupe($questions);
You'll need to modify 392299 above to be the ID of the question you want to make sticky - you can see this from its URL.