Here is a one-liner using a slight variation on your "x" theme:

$ cat nums.txt
20188
18350
4005
127736
10291
4937
57500
150494

$ perl "-F *" -ape "s//$|x(11-@F)/e" nums.txt
0000020188
0000018350
0000004005
0000127736
0000010291
0000004937
0000057500
0000150494
[download]

-- Dave :-)