Hmm - on this machine, with this perl, your suggestion does not work, and I think it does not work while used in the same block, as use is a compile time thing:

Q:\>perl -v

This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)
(snip-snap)

Q:\>perl -e "$foo='bar'; use lib $foo; die join ';',@INC"
Empty compile time value given to use lib at -e line 1
;s:/Os/OSP/OSPI/Perl/lib;s:/Os/OSP/OSPI/Perl/site/lib;. at -e line 1.

Q:\>perl -e "BEGIN{$foo='bar'; use lib $foo;} die join ';',@INC"
Empty compile time value given to use lib at -e line 1
;s:/Os/OSP/OSPI/Perl/lib;s:/Os/OSP/OSPI/Perl/site/lib;. at -e line 1.

Q:\>perl -e "BEGIN{$foo='bar';} use lib $foo; die join ';',@INC"
bar;s:/Os/OSP/OSPI/Perl/lib;s:/Os/OSP/OSPI/Perl/site/lib;. at -e line 
+1.

Q:\>perl -e "BEGIN{my $foo='bar'; eval qq{use lib $foo;}};die join ':'
+,@INC"
bar:s:/Os/OSP/OSPI/Perl/lib:s:/Os/OSP/OSPI/Perl/site/lib:. at -e line 
+1.
[download]

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
[download]