problem with perl versions

[RJ45]

I am runing freebsd 5.1

I have a problem with perl versions
I need to use perl 5.8.0 but everytime I install from ports a application
which depends from perl 5.6 something is overwritten and perl 5.8.0 is not
avalaible and I have to "make reinstall" perl 5.8.0 every time.
Is there a way to set a system variable for perl5.8.0 as default?

I also tryed with this in /etc/make.conf

PERL_VER=5.8.0
PERL_VERSION=5.8.0


but it is useless. if I then install an application from ports which uses
perl5.6 the default perl becomes perl 5.6 regardless of make.conf
settings.

thank you very much

Rick