How to install pkg in a non-standard location? (OS X)

Question

In brief, my question is this:

How can I install an OS X framework from a *.pkg file somewhere other than under /Library/Frameworks (or /System/Library/Frameworks)?

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Background

I want to install a version of Python 2.7.3 that lives under $HOME/Library/Frameworks/Python.framework and $HOME/python.

My goal here is to have a version of Python that is as independent as possible from the Python that comes with OS X Lion.

Among the problems I am trying to avoid by doing this is the buggy Tk framework that comes with the latest versions of OS X.

Therefore, a key sub-goal here is to install new Tcl and Tk frameworks, separate from the system-supplied ones. The ones I want to install come from ActiveState ("Mac OS X (10.5+, x86_64/x86)"), in the form of a *.pkg file.

When I click on this file, I get presented with the usual "wizard"-like sequence of steps ("Introduction", "License", etc.). At no point during this sequence I am offered the opportunity to choose a different installation location for these frameworks before I reach the choice of clicking on the INSTALL button.¹

I suspect that if I click on this button, the installed files will go under /Library/Frameworks (or possibly under /System/Library/Frameworks), which is what I'm trying to avoid. (Indeed, when I click on INSTALL, I'm immediately presented with an password-entry dialog, which is a pretty good indication that the installation will put files somewhere under /Library or /System.)

Therefore I'm looking for an alternative way to perform this installation that will allow me to explicitly set the destination folder for the installed files.

_{¹Yes, the installer allows me choose a different volume for the installation, but it does not let me specify, e.g., $HOME/Library/Frameworks as the destination for the installed files.}