Sorry, Image::Magick hasn't what you are looking for; you can of course build your own system using QueryFontMetrics; here is an example of its usage:

#!/usr/bin/perl

use Image::Magick;

$i = Image::Magick->new;
$i->Set( size => '320x200' );
$i->ReadImage('xc:white');

@params = ( font      => '@arial.ttf',
            text      => 'some text',
            pointsize => 36 );

($w, $h,
 $ascend, $descend,
 $text_w, $text_h,
 $max) = $i->QueryFontMetrics( @params );
print "$w, $h, $ascend, $descend, $text_w, $text_h, $max\n";

$i->Annotate( @params,
              stroke  => red,
              fill    => red,
              gravity => center );

$i->Display;
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