thanks guys, it seems that editing both config.pm and config_heavy.pl 's perl path will work.

here are the steps in point form in case others need it :
(below is based on assumption your shebang is #!/usr/bin/perl, and that you want to move perl to another location while retaining strawberry's compilers in strawberry folder)

1. Move bin, lib and site folder of strawberry/perl/ to c:/usr/
2. Edit usr/lib/config_heavy.pl and change all reference of strawberry's perl to usr.

for example :
archlib='C:\strawberry\perl\lib'

change to :
archlib='C:\usr\lib'

note : but for those that's not related to perl, don't change it unless u plan to move strawberry. Examples are :

incpath='C:\strawberry\c\include'

3. Edit usr/lib/config.pm as well.
*same as point 2.

4. Make sure the PATH environment is pointing to usr/bin.
you should then be able to use strawberry perl properly without errors.