Remember: the value of $/ is a string, not a regex. awk has to be better for something. :-)

Ok - so my suggestion would be to slurp in the entire thing and then split on your regex.

local $/ = undef;
my $record = <INPUT>;
my @chunks = split /regex/ , $record;
for my $chunk ( @chunks ) {
    my @lines = split /\n/ , $chunk;
}
[download]

Update: If for some reason you need to keep the header information - do something like this:

local $/ = undef;
my $record = <INPUT>;
my @chunks = split /(regex)/ , $record;
while ( @chunks ) {
    my $header = shift;
    my $chunk = shift;
    my @lines = split /\n/ , $chunk;
}
[download]