Forcing Capitalization with PHP

[Lotus28]

I am using this simple php code to force thread titles to capitalize the first letter of each word:

$smallwords = array( 'a','of','the');

$words = explode(' ', $vbulletin->GPC['subject']);

foreach ($words as $key => $word) {
    if (!$key or !in_array($word, $smallwords)) $words[$key] = ucwords($word);
 }
 
$vbulletin->GPC['subject'] = implode(' ' , $words);

I also want to be able to force certain words to be ALL CAPS in the title... do you know what I would need to add to this code to specify certain words so that they will always be caps when displayed in the titles? Thanks!