...
my %min_version = (Some/Place/Foo.pm => 0.06, # need at least version 0.06 of Some::Place::Foo
                   Other/Spot/Bar.pm => 1.35, # need at least version 1.35 of Other::Spot::Bar
                   Baz.pm            => 2.72, # need at least version 2.72 of Baz
                   );  

my @prereqs;

for(keys(%min_version)) {
  eval {require $_};
  # Ignore modules that don't load.
  unless($@){
    my $m = $_;
    $m =~ s/\//::/g;
    $m =~ s/\.pm$//;
    my $v = $min_version{$_};
    push @prereqs($m, $v);
  }
}

my %h = @prereqs;
....

##</code><code>##

...
'PREREQ_PM' => \%h,
...