that you could force a failure of the regexp

It's probably the 'empty negative lookahead' (?!) :

 ...
 my @nums = 1 .. 30;
 my $reg = qr{^(\d+)$ (??{ $1 % 3 ? '(?!)' : '' })}x;
 print join ',', grep /$reg/, @nums;
 ...
[download]

This is documented eg. in Jeff Pinyan's work (also here on perlmonks).

_{Correction 1: Added bounds "^ $" to \d+ to prevent backtracking in the above example.}

_{Correction 2: backtracking can be prevented by the atomic group (?>...):}

 ...
 my $reg = qr{ ^((?>\d+)) (??{ !!($1 % 3) and '(?!)' }) }x;
 ...
[download]

Regards

mwa