There is a built in search library in the code, but we don't have it exposed through the extension. That is probably the cleanest solution.
A quick fix would be to write some code to loop through it like:
<?php
$wagespaid = new WA_MySQLi_RS("wagespaid",$horizon_i,1);
$wagespaid->setQuery("SELECT SUM(Amount) AS sAmount FROM WagesPaid WHERE 1=0");
for ($x=0; isset($_GET['Week']) && $x<sizeof($_GET['Week']); $x++) {
$wagespaid->Statement = $wagespaid->Statement . " OR Concat(',',WagesPaid.Weeks,',') LIKE '%,".intval($_GET['Week'][$x]).",%'";
}
$wagespaid->bindParam("sl", "".implode(",",) ."", "-1");
$wagespaid->execute();
?>