You can still use a lexical but you have to be explicit about what is being matched, also taking care with the difference in precedence of and and &&. With lower precedence and:-

$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<EOD or die $!;
Seb
Xavier
Peter

Roland
Jim
Xerox
Paddle

Yoyo
EOD

while ( my $line = <$inFH> )
{
    print $line
       if $line =~ m{X} .. $line =~ m{^\s*$} and $line !~ m{^\s*$};
}'
Xavier
Peter
Xerox
Paddle
$
[download]

Higher precedence && requires parentheses:-

$ perl -Mstrict -Mwarnings -E '
open my $inFH, q{<}, \ <<EOD or die $!;
Seb
Xavier
Peter

Roland
Jim
Xerox
Paddle

Yoyo
EOD

while ( my $line = <$inFH> )
{
    print $line
       if ( $line =~ m{X} .. $line =~ m{^\s*$} ) && $line !~ m{^\s*$};
}'
Xavier
Peter
Xerox
Paddle
$
[download]