Why not do:

my $base_class = '...'; # base class for exceptions
my $error_class = '...'; # my error class

sub fixerror(;$) {
    my $e = @_ ? $_[0] : $@;

    return $e
        if blessed( $e ) && $e->isa( $base_class );

    return $error_class->new( $e );
}

sub try(&) {
    my $code = $_[0];

    eval { &$code() };

    $@ ? fixerror($@) : undef;
}
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That way you don't have a callback that has the potential of getting called multiple times.