There was and will never be possible, sorry. They're too many difference between a x86 and x64 version. A hack would mean re-making the whole windows, that's simply impossible to do and would take month or years for a single programmer to do. It's easier and faster to start a fresh install.
The only partly way is to use WET (Windows Easy Transfer)! You can save the 32 bit apps but not the 64 bit or the drivers!
It won't work even if you replace every exe, library and driver with the 32 bit version (there are other differences, too, such as parts of the file structure, registry structure, the 32-bit subsystem, ...).
In main WET is for to move programs and settings from one OS (Vista and/or Windows 7 and with limitations Windows XP) to an other OS regardless of up- or downgrading. I was use it once on an customers computer with 64 bit Vista for to get the installed 32 bit app's working on an "downgraded" 32 bit Vista because I didn't had the original app's which were in Germany and the Laptop of my customer here in Thailand!! It worked and I do believe it will work in Windows 7 as well.