forcing ports to use Perl 5.8.8

[rihad]

Hello, I need to install security/p5-Digest-HMAC from the ports, but 
_only_ with the currently installed Perl 5.8.8, without it being 
upgraded to 5.8.9 as a dependency (because some other software dumps 
core with Perl 5.8.9). How can I as a user cleanly tell the system to 
stay with 5.8.8 and still be able to upgrade any other port, even all of 
them? I have in /etc/make.conf:

PERL_VER=5.8.8
PERL_VERSION=5.8.8

but this isn't enough.
/usr/ports/Mk/bsd.perl.mk has several knobs, which ones can I set in 
/etc/make.conf to achieve what I need (stay with perl 5.8.8)?

TIA