Here's one resolution:

1. Edit setup.py to make INCLUDE/LIB paths for OpenSSL use the SDKROOT (for 10.5+ compat):
[...]
search_for_ssl_incs_in = ["/Developer/SDKs/MacOSX10.5.sdk/usr/include/" if ON_SNOW_LEOPARD else "/usr/include"]
search_for_ssl_libs_in = ["/Developer/SDKs/MacOSX10.5.sdk/usr/lib/" if ON_SNOW_LEOPARD else "/usr/lib"]

2. Force the 10.5 SDK to use Apple's Tcl/Tk 8.5 (10.5 users must install ActiveTcl, and then launch Python as "arch -i386 python2.7" if they want to use tkinter):

$ sudo ln -s /System/Library/Frameworks/Tcl.framework /Developer/SDKs/MacOSX10.5.sdk/Library/Frameworks/

$ sudo ln -s /System/Library/Frameworks/Tk.framework /Developer/SDKs/MacOSX10.5.sdk/Library/Frameworks/

3. Build with 10.5 SDK

$ export MACOSX_DEPLOYMENT_TARGET=10.5
$ ./configure --enable-framework --enable-universalsdk=/Developer/SDKs/MacOSX10.5.sdk/ --with-universal-archs=intel
$ make

And the result is a Python that works on 10.5+ and gives you 64-bit Tkinter for 10.6 users.

This is how I am intending to build ActivePython 2.7 this weekend.