Suggestion: try plenv - it makes it simple to install and use other Perls apart from the system Perl (this is generally much safer than tinkering with the system Perl).

It is easy to install

Once you've done that, you can use it to install cpan minus

plenv install-cpanm
[download]

Then

% cpanm File::TreeBuilder  
--> Working on File::TreeBuilder
Fetching http://www.cpan.org/authors/id/L/LU/LUCS/File-TreeBuilder-0.0
+2.tar.gz ... OK
Configuring File-TreeBuilder-0.02 ... OK
==> Found dependencies: Test::Usage
--> Working on Test::Usage
Fetching http://www.cpan.org/authors/id/L/LU/LUCS/Test-Usage-0.08.tar.
+gz ... OK
Configuring Test-Usage-0.08 ... OK
==> Found dependencies: IO::Capture::Stderr, File::Slurp, IO::Capture:
+:Stdout
--> Working on IO::Capture::Stderr
Fetching http://www.cpan.org/authors/id/R/RE/REYNOLDS/IO-Capture-0.05.
+tar.gz ... OK
Configuring IO-Capture-0.04 ... OK
Building and testing IO-Capture-0.05 ... OK
Successfully installed IO-Capture-0.05
--> Working on File::Slurp
Fetching http://www.cpan.org/authors/id/C/CA/CAPOEIRAB/File-Slurp-9999
+.32.tar.gz ... OK
Configuring File-Slurp-9999.32 ... OK
Building and testing File-Slurp-9999.32 ... OK
Successfully installed File-Slurp-9999.32
Building and testing Test-Usage-0.08 ... OK
Successfully installed Test-Usage-0.08
Building and testing File-TreeBuilder-0.02 ... OK
Successfully installed File-TreeBuilder-0.02
4 distributions installed
[download]