i'd use one of the custom fields, which then allows the user to turn that on/off by him/herself. then turn on this field in user settings via your admin cpanel and name it 'AllowRated' (or like that).
then just change the if to NOT be by user number, but by the custom field value. ie: 0,1 or null/whatever (prolly)
this would then allow any number of users to essentially allow the in place ratings to be applied as they permit.
the test would be then if (($config['USER_RATINGS'] == "1") && (!$user['custom_fieldx'])) { no rates } else { do rate }; <-- totally pseudo code there, so don't kill me

ps: i'm doing this at WORK (shhhh don't tell anyone), so it's from memory, but if i get home and you don't have a solution, i will at least copy/paste the exact code and/or steps (that i might use) here to accomplish this .
pps: you could even go further as to allow a tri-state condition where users are of 3 minds:
0 - No rates never! (head in the sand)
1 - No one else sees my rating, but me (curious)
2 - Rate me hard baby (let 'er rip)
then to make it idiot proof in the profiles, replace the text field with a 3 state radio button (defaulted to most common) where users choose 0, 1 or 2 (with languages descriptors, of course)

[humor mode on]
ppps: hehe, i just had a thought. the options could be expanded to:
0 - Nobody can see my rating and I don't wanna look (scared)
1 - Peeps can see my rating! But i wanna put a fake 5 in there (vain)
2 - Peeps can see my rating! But i wanna put a fake 0 in there (anti establishment)
3 - Peeps can see my rating! But i wanna put a fake 3 in there (lurker)
4 - Peeps can rate me, but not see! But i wanna peek (curious)
5 - Rate me hard baby! (muhaha)
[/humor]
