... path happens to be the current path of the script plus /lib ...

If the directory you want to add is a fixed and existing sub-directory of the script directory, I don't understand why lib won't work:

c:\@Work\Perl\monks\dougbot>perl -wMstrict -le
"use lib './junque';
 local $\" = qq{'\n'};
 print qq{'@INC'};
"
'./junque'
'C:/strawberry/5.14/perl/site/lib'
'C:/strawberry/5.14/perl/vendor/lib'
'C:/strawberry/5.14/perl/lib'
'.'

c:\@Work\Perl\monks\dougbot>dir
...
12/04/2013  02:35 PM    <DIR>          .
12/04/2013  02:35 PM    <DIR>          ..
12/04/2013  02:06 PM             9,730 array_disjunct_1.pl
12/04/2013  02:35 PM    <DIR>          junque
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