How about something like this:

sub f{
  my $t=0;
  $t+=rand() for(1..5);
  return int($t*20+1);
}
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You can vary the number of iterations (1..5) and scaling factor (20) based on the exact distribution curve you want.

There are several other ways to approach this problem. If efficiency were of paramount importance, I would try using statistical method to derive a function that would aproximate the curve of how in frequency you would map numbers from 0 to 0.9999 (the range of perl's rand function) into the range you want (1 to 100).