$ perl -I" a b c d " -le"print for @INC"
 a b c d
C:/perl/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/5.10.1/lib
C:/perl/site/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/site/5.10.1/lib
.

$ set PERL5LIB=THE STUFF

$ perl -I1 -I2 -I3 -I4 -le"print for @INC"
1
2
3
4
THE STUFF
C:/perl/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/5.10.1/lib
C:/perl/site/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/site/5.10.1/lib
.

$ perl -Mlib="blah blah blah" -le"print for @INC"
blah blah blah
THE STUFF
C:/perl/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/5.10.1/lib
C:/perl/site/5.10.1/lib/MSWin32-x86-multi-thread
C:/perl/site/5.10.1/lib
.