Another way:

use Data::Dumper;

use strict;
use warnings;

my $params = "option1 = value0 value1 value2 option3 =value3 value4 op
+tion2=value5";
$params =~ s/\s*=\s*/=/g;
my @params = split /\s+/, $params;
my %params;
my $cur_val;
for my $param (@params) {
    my @pairs = split /=/, $param;
    $cur_val = $pairs[0] if ($#pairs) ;
    push @{$params{$cur_val}}, $pairs[-1];
}
print Dumper(\%params);
[download]

Which gives:

$VAR1 = {
          'option1' => [
                         'value0',
                         'value1',
                         'value2'
                       ],
          'option3' => [
                         'value3',
                         'value4'
                       ],
          'option2' => [
                         'value5'
                       ]
        };
[download]