Your suggestion works ... but the question was a bit more complicated because $temp = 'foo$1bar'. And then the simple evaluation doesn't work ... you have to employ a little extra trick (proposed by japhy a couple of days ago):

$temp0="ZO";
$temp1='foo$1bar';
$x="ABCZO";
$x =~ s/([A-Za-z]+)$temp0/qq[qq[$temp1]]/ee;  
print $x; # prints fooABCbar
[download]

-- Hofmator