handling dependency for mod_perl under Apache 2.0 and 2.2 within port?

[Vivek Khera]

How does one handle the dependency list in the port for a port which  
needs mod_perl, but doesn't care if it is in apache 2.0 or 2.2.

In apache 2.2 modperl is installed in /usr/local/libexec/apache22/ 
mod_perl.so, and in apache 2.0, /usr/local/libexec/apache2/mod_perl.so.

I don't see in bsd.apache.mk any way to find what that libexec  
subdirectory name should be.

Any advice?  Thanks!