Unless you're dealing with enormous datasets, you can just use permutation for p-values, e.g. (untested):

use List::Util 'shuffle';
$rSquared = $lfit->setData($xref, $yref)->rSquared;
@rsq = map { $lfit->setData($xref, [shuffle @$yref])->rSquared } 1..10
+00;

print "pretty good\n" if (grep { $_ > $rSquared } @rsq) > 950;
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