You would have to duplicate the /shift alias as /shift2 and alter it to do what you want.
Alternatively, you could do something like this:
F1 {
close -m $active
if ($query(0) <= 0) window -a $+(",$query(1),")
else shift 1
}
This code will go to the FIRST query if one exists, else it will scroll to a channel window.
-genius_at_work