Override package dependency in pkgsrc?

[AGC <agcarver+netbsd%acarver.net@localhost>]

I can't seem to figure out why python 2.6 is segfaulting during a 
compile of one of the test programs.

Is there a way to force pkgsrc to skip downloading that one particular file?

Otherwise, how do I tell the scons build in pkgsrc to use the currently 
installed python2.4 instead of python2.6?

When I start a make inside pkgsrc I get the message:

==========================================================================
The following variables will affect the build process of this package,
scons-1.3.1.  Their current value is shown below:

        * PYTHON_VERSION_DEFAULT = 26

Based on these variables, the following variables have been set:

        * PYPACKAGE = python26

You may want to abort the process now with CTRL-C and change their value
before continuing.  Be sure to run `/usr/bin/make clean' after
the changes.
==========================================================================

I'm just not sure where to change them.  I _think_ basic scons will work 
with python2.4.  If I can get around the one compile error in 2.6 I'll 
use it instead.