you could modify in qa-include/qa-db-selects.php file the line 1269
from :
'source' => '^users JOIN (SELECT userid FROM ^userpoints ORDER BY points DESC LIMIT #,#) y ON ^users.userid=y.userid JOIN ^userpoints ON ^users.userid=^userpoints.userid',
to :
'source' => '^users JOIN (SELECT userid FROM ^userpoints ORDER BY points DESC LIMIT #,#) y ON ^users.userid=y.userid JOIN ^userpoints ON ^users.userid=^userpoints.userid WHERE ^users.handle not in ("admin","admin2")',
where admin, admin2, etc... are the usernames you want to exclude.
Or, if you prefer to use id :
WHERE ^users.userid not in (1,2)
where 1,2 are the id of the users you want to exclude.
ps
consider that it would be a good practice to write a plugin instead of modifying the core, but I'm not able to do it yet