this works

use PDL;

my $pdl1 = pdl(
 [  2.7650514,          0,          0,          0,          0,       0
+,          0],
 [0,   1.2905497,          0,           0,           0,        0,     
+      0],
 [          0,           0,  0.54930597,           0,        0,       
+    0,           0],
 [          0,           0,           0,  0.23264228,           0,    
+       0,           0],
 [          0,          0,       0,           0,  0.19463077,         
+  0,           0],
 [          0,       0,           0,           0,           0,  0.1666
+9291,           0],
 [       0,           0,           0,           0,           0,       
+    0, 0.095157451]);

my $pdl2 = zeroes(27,7);
$pdl1=transpose($pdl1);

$pdl3 = $pdl1->append($pdl2);

$pdl3=transpose($pdl3);
print $pdl3;
[download]

Append appends along the first dimension, so you have to transpose first, then transpose back afterwards.