$dbh->quote() only takes one argument:
$quoted_string = $dbh->quote($string);

Validating against \d+ seems perfectly reasonable to me, since I can't think of any way to do it using DBI. (Placeholders don't work in LIMIT, IIRC, but you could try that.)

Update: oops, reading further down the docs, quote does allow two arguements. However, quote() quotes (makes safe), it does not validate (makes valid).