You would need to hand edit the code to force the double quotes around the search value. The code for a keyword search will look similar to:
$WADbSearch1->keywordComparison($KeyArr1,"".((isset($_GET["S_ProductName"]))?$_GET["S_ProductName"]:"") ."","WHERE","Includes",",%20","%20","%22","%22",0);
if you where to edit that to:
$WADbSearch1->keywordComparison($KeyArr1,"".((isset($_GET["S_ProductName"]))?"\"".$_GET["S_ProductName"]."\"":"") ."","WHERE","Includes",",%20","%20","%22","%22",0);
it will force a double quote around any search term you enter.